#include<iostream>
#include<fstream>
using namespace std;
int p,p5,n;

int putere5(int x) {
    int t=0;
    while (x%5==0)
    {
        t++;
        x=x/5;
    }
    return t;
}

int main(){
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>p;
    n=0; p5=0;
    while (p5<p) {
        n=n+5;
        p5=p5+putere5(n);
    }
    g<<n;

    f.close();
    g.close();
    return 0;
}