Given a range L and R, the task is to find the sum of all natural numbers in range L to R. **Examples**:

Input:L = 2, R = 5Output:14 2 + 3 + 4 + 5 = 14Input:L = 10, R = 20Output:165

A **naive approach **is to traverse from L to R and add all the elements one by one to get the sum.

An **efficient approach** is to use the formula for the sum of first N natural numbers. The idea of the inclusion-exclusion principle helps to solve the above problem. Find the sum of natural numbers till **R** and **L-1** and then subtract **sum(R)-sum(l-1)****.**

Below is the implementation of the above approach:

## C++

`// C++ program to print the sum` `// of all numbers in range L and R` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to return the sum of` `// all natural numbers` `int` `sumNatural(` `int` `n)` `{` ` ` `int` `sum = (n * (n + 1)) / 2;` ` ` `return` `sum;` `}` `// Function to return the sum` `// of all numbers in range L and R` `int` `suminRange(` `int` `l, ` `int` `r)` `{` ` ` `return` `sumNatural(r) - sumNatural(l - 1);` `}` `// Driver Code` `int` `main()` `{` ` ` `int` `l = 2, r = 5;` ` ` `cout << ` `"Sum of Natural numbers from L to R is "` ` ` `<< suminRange(l, r);` ` ` `return` `0;` `}` |

## Java

`// Java program to print the sum` `// of all numbers in range L and R` `class` `GFG{` `// Function to return the sum of` `// all natural numbers` `static` `int` `sumNatural(` `int` `n)` `{` ` ` `int` `sum = (n * (n + ` `1` `)) / ` `2` `;` ` ` `return` `sum;` `}` `// Function to return the sum` `// of all numbers in range L and R` `static` `int` `suminRange(` `int` `l, ` `int` `r)` `{` ` ` `return` `sumNatural(r) - sumNatural(l - ` `1` `);` `}` `// Driver Code` `public` `static` `void` `main(String[] args)` `{` ` ` `int` `l = ` `2` `, r = ` `5` `;` ` ` `System.out.println(` `"Sum of Natural numbers from L to R is "` `+suminRange(l, r));` `}` `}` `// This code is contributed by mits` |

## Python3

`# Python3 program to print the sum of` `# all numbers in range L and R` `# Function to return the sum of all natural numbers` `def` `sumNatural(n):` ` ` `sum` `=` `(n` `*` `(n` `+` `1` `))` `/` `/` `2` ` ` `return` `sum` `# Function to return the sum` `# of all numbers in range L and R` `def` `suminRange(l, r):` ` ` `return` `sumNatural(r) ` `-` `sumNatural(l` `-` `1` `)` `# Driver Code` `l ` `=` `2` `; r` `=` `5` `print` `(` `"Sum of Natural numbers from L to R is "` `,suminRange(l, r))` `# This code is contributed by Shrikant13` |

## C#

`// C# program to print the sum` `// of all numbers in range L and R` `using` `System;` `class` `GFG` `{` `// Function to return the sum` `// of all natural numbers` `static` `int` `sumNatural(` `int` `n)` `{` ` ` `int` `sum = (n * (n + 1)) / 2;` ` ` `return` `sum;` `}` `// Function to return the sum` `// of all numbers in range L and R` `static` `int` `suminRange(` `int` `l, ` `int` `r)` `{` ` ` `return` `sumNatural(r) -` ` ` `sumNatural(l - 1);` `}` `// Driver Code` `static` `public` `void` `Main ()` `{` ` ` `int` `l = 2, r = 5;` ` ` `Console.WriteLine(` `"Sum of Natural numbers "` `+` ` ` `"from L to R is "` `+` ` ` `suminRange(l, r));` `}` `}` `// This code is contributed by akt_mit` |

## PHP

`<?php` `// PHP program to print the sum` `// of all numbers in range L and R` `// Function to return the sum of` `// all natural numbers` `function` `sumNatural(` `$n` `)` `{` ` ` `$sum` `= (` `$n` `* (` `$n` `+ 1)) / 2;` ` ` `return` `$sum` `;` `}` `// Function to return the sum` `// of all numbers in range L and R` `function` `suminRange(` `$l` `, ` `$r` `)` `{` ` ` `return` `sumNatural(` `$r` `) -` ` ` `sumNatural(` `$l` `- 1);` `}` `// Driver Code` `$l` `= 2;` `$r` `= 5;` `echo` `"Sum of Natural numbers "` `.` ` ` `"from L to R is "` `,` ` ` `suminRange(` `$l` `, ` `$r` `);` `// This code is contributed by ajit` `?>` |

## Javascript

`<script>` `// JavaScript program to print the sum` `// of all numbers in range L and R` `// Function to return the sum of` `// all natural numbers` `function` `sumNatural(n)` `{` ` ` `sum = (n * (n + 1)) / 2;` ` ` `return` `sum;` `}` `// Function to return the sum` `// of all numbers in range L and R` `function` `suminRange(l, r)` `{` ` ` `return` `sumNatural(r) -` ` ` `sumNatural(l - 1);` `}` `// Driver Code` `let l = 2;` `let r = 5;` `document.write(` `"Sum of Natural numbers from L to R is "` `+` ` ` `suminRange(l, r));` `// This code is contributed by sravan kumar gottumukkalan` `</script>` |

**Output:**

Sum of Natural numbers from L to R is 14

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