#include <stdio.h>
#include <stdlib.h>


int findTrailingZeros(long long  n);
int calc(int n);

int main()
{
    FILE* in = fopen("fact.in","r");
    FILE* out = fopen("fact.out","r");
    int n;
    fscanf(in,"%d",&n);

    int c = findTrailingZeros(n);
    fprintf(out, "%d",c);
    return 0;
}

int findTrailingZeros(long long  n)
{
    // Initialize result
    int count = 0;
    int i=5;
    // Keep dividing n by powers of 5 and update count
    for (i=5; n/i>=1; i *= 5)
          count += n/i;

    return count;
}