Given a number **N**. The task is to find the permutation **P** of first **N** natural numbers such that sum of **i % P _{i}** is maximum possible. The task is to find the maximum possible sum not it’s permutation.

**Examples:**

Input:N = 5Output:10

Possible permutation is 2 3 4 5 1.

Modulus values will be {1, 2, 3, 4, 0}.

1 + 2 + 3 + 4 + 0 = 10

Input:N = 8Output:28

**Approach:** Maximum possible sum is **(N * (N – 1)) / 2** and it is formed by the permutation **2, 3, 4, 5, ….. N, 1**.

Below is the implementation of the above approach:

`// C++ implementation of the approach ` `#include <bits/stdc++.h> ` `using` `namespace` `std; `
` ` `// Function to find the permutation of ` `// the first N natural numbers such that ` `// the sum of (i % Pi) is maximum possible ` `// and return the maximum sum ` `int` `Max_Sum(` `int` `n) `
`{ ` ` ` `return` `(n * (n - 1)) / 2; `
`} ` ` ` `// Driver code ` `int` `main() `
`{ ` ` ` `int` `n = 8; `
` ` ` ` `// Function call `
` ` `cout << Max_Sum(n); `
` ` ` ` `return` `0; `
`} ` |

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`// Java implementation of the approach ` `class` `GFG `
`{ ` ` ` `// Function to find the permutation of ` `// the first N natural numbers such that ` `// the sum of (i % Pi) is maximum possible ` `// and return the maximum sum ` `static` `int` `Max_Sum(` `int` `n) `
`{ ` ` ` `return` `(n * (n - ` `1` `)) / ` `2` `; `
`} ` ` ` `// Driver code ` `public` `static` `void` `main (String[] args) `
`{ ` ` ` `int` `n = ` `8` `; `
` ` ` ` `// Function call `
` ` `System.out.println(Max_Sum(n)); `
`} ` `} ` ` ` `// This code is contributed by Rajput-Ji ` |

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`# Python3 implementation of the approach ` ` ` `# Function to find the permutation of ` `# the first N natural numbers such that ` `# the sum of (i % Pi) is maximum possible ` `# and return the maximum sum ` `def` `Max_Sum(n) : `
` ` ` ` `return` `(n ` `*` `(n ` `-` `1` `)) ` `/` `/` `2` `; `
` ` `# Driver code ` `if` `__name__ ` `=` `=` `"__main__"` `: `
` ` ` ` `n ` `=` `8` `; `
` ` ` ` `# Function call `
` ` `print` `(Max_Sum(n)); `
` ` `# This code is contributed by AnkitRai01 ` |

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`// C# implementation of the approach ` `using` `System; `
` ` `class` `GFG `
`{ ` ` ` `// Function to find the permutation of ` `// the first N natural numbers such that ` `// the sum of (i % Pi) is maximum possible ` `// and return the maximum sum ` `static` `int` `Max_Sum(` `int` `n) `
`{ ` ` ` `return` `(n * (n - 1)) / 2; `
`} ` ` ` `// Driver code ` `public` `static` `void` `Main (String[] args) `
`{ ` ` ` `int` `n = 8; `
` ` ` ` `// Function call `
` ` `Console.WriteLine(Max_Sum(n)); `
`} ` `} ` ` ` `// This code is contributed by Princi Singh ` |

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**Output:**

28

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