#include <stdio.h>
#include <math.h>
#include <iostream>

using namespace std;
int intlog(double base, double x) {
    return (int)(log(x) / log(base));
}
int k,j;
unsigned long S,n;

FILE*f=fopen("fact.in","r");
FILE*g=fopen("fact.out","w");
int main()
{
    scanf("%lu",&n);

    S=0;
    k=intlog(5,n);
    for(j=1;j<=k;j++)
        {
        S=S+n/pow(5,j);
        }
    fprintf(g,"%lu ",S);

    fclose(f);
    fclose(g);
    return 0;
}