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C# Program to Count trailing zeroes in factorial of a number
• Last Updated : 02 Jan, 2019

Given an integer n, write a function that returns count of trailing zeroes in n!.

Examples :

```Input: n = 5
Output: 1
Factorial of 5 is 120 which has one trailing 0.

Input: n = 20
Output: 4
Factorial of 20 is 2432902008176640000 which has
4 trailing zeroes.

Input: n = 100
Output: 24
```
```Trailing 0s in n! = Count of 5s in prime factors of n!
= floor(n/5) + floor(n/25) + floor(n/125) + ....
```

## C#

 `// C# program to count ` `// trailing 0s in n! ` `using` `System; ` ` `  `class` `GFG { ` ` `  `    ``// Function to return trailing ` `    ``// 0s in factorial of n ` `    ``static` `int` `findTrailingZeros(``int` `n) ` `    ``{ ` `        ``// Initialize result ` `        ``int` `count = 0; ` ` `  `        ``// Keep dividing n by powers ` `        ``// of 5 and update count ` `        ``for` `(``int` `i = 5; n / i >= 1; i *= 5) ` `            ``count += n / i; ` ` `  `        ``return` `count; ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``int` `n = 100; ` `        ``Console.WriteLine(``"Count of trailing 0s in "`  `                ``+ n + ``"! is "` `+ findTrailingZeros(n)); ` `    ``} ` `} ` ` `  `// This code is contributed by vt_m `

Output:

```Count of trailing 0s in 100! is 24
```

Please refer complete article on Count trailing zeroes in factorial of a number for more details!

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