// 2019 IUSB Programming Competition
// Round 1 Problem 3
// Count the number of training 0s in n!
// Solution by Liguo Yu

#include <iostream>
using namespace std;

int main()
{
	int num;
	
	cin >> num;
	
	int count = 0;
	
	for (int i = 5; num / i >= 1; i = i * 5)
	{
		count = count + num / i;
	}
	
	cout << count;
	
	return 0;
}