/*
	Finding number of tailing zeros of n!
	@Author: md.moniruzzaman
*/

#include<stdio.h>
#define maxn 1000000

char Flag[maxn+1];
int Prime[79000], totalPrime;



int CountFactor(int n, int p) {
	int count = 0;
	for(int i = p; i<= n; i *= p) {
		count += n/i;
	}
	return count;
}

void findZeros(int n) {
	int numberOf5;
	numberOf5 = CountFactor(n,5);
	printf("%d\n",numberOf5);
}

void main() {
	int n;
	scanf("%d",&n);
	findZeros(n);
}