#pragma GCC optimize ("03,unroll-loops")
#include <bits/stdc++.h>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");


int main(int argc, char const *argv[])
{
    long long int sol = 0;
    int p;
    fin>>p;
    if( p == 0 )
    {
        fout<<1;
        return 0;
    }
    for(int i=1;i<=p;i++){
        sol+=5;
        int j=i;
        while(j%5==0){
            i++;
            j/=5;
        }
    }
    fout<<sol;
    return 0;
}