#include <iostream>
#include <vector>
#include <algorithm>
#include <fstream>
using namespace std;

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

int main()
{
    long p , mijl, src;
    in>>p;
    long res(-1);
    long start(1), stop(1000000000);
    while (start <=stop){
        mijl = (start+stop)/2;
        src = 0;
        for (int q = 5; q <=mijl; q*=5){
            src += (mijl/q);
        };
        if (src == p){
            res = mijl;
            stop = mijl - 1;
        } else if (src > p){
            stop = mijl - 1;
        } else {
            start = mijl + 1;
        };
    };
    out<<res;
}