#include <iostream>
#include <fstream>

using namespace std;

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

long long r(-1), s(1), f(100000000), p, mijl, zr;

int main()
{
    in>>p;
    while (s <= f){
        mijl = (s+f)/2;
        zr = 0;
        for (int q = 5; q <= mijl; q*= 5){
            zr += (mijl/q);
        };
        if (zr == p){
            r = mijl;
            f = mijl-1;
        } else if (zr > p){
            f = mijl - 1;
        } else s = mijl + 1;
    };
    out<<r;
    return 0;
}