lastzero.c

#include<stdio.h>

#define long long long
#define nln '\n'

int main()
{
    long n;
    scanf("%lli", &n);
    long fiv = 1, res = 0;
    while (fiv <= n){
        fiv *= 5;
        res += n / fiv;
    }
    printf("%lli\n", res);
    return 0;
}