#include <iostream>
#include <fstream>

using namespace std;

ifstream in("factorial.in");
ofstream out("factorial.out");

int main() {
    long long int p, z=0;
    in>>p;
    if (p==0) {
        out<<1;
        return 0;
    }
    for (int n=0; ; n+=5) {
        z = 0;
        for (int i=5; i<=n; i*=5) z+=n/i;
        if (z == p) {
            out<<n;
            return 0;
        }
    }
}