#include <iostream>
#include <fstream>
using namespace std;
ifstream fu("factorial.in");
ofstream fo("factorial.out");
int main()
{
    long capat , inceput ,  p , n , k ;
    fu >> n;
    capat = 400000015;
    p = capat / 2 ;
    inceput = 1;
    while (p){
        p=(inceput+capat)/2;
        if (p % 5 == 1) p=p-1;
        if (p % 5 == 2) p=p-2;
        if (p % 5 == 3) p=p-3;
        if (p % 5 == 4) p=p-4;
        k = p/5+p/25+p/125+p/625+p/3125+p/15625+p/78125+p/390625+p/1953125+p/9765625+p/48828125+p/244140625;
        if (k==n) break;
        if (k>n){
        capat = p;
        }
        if (k<n){
            if (inceput == p) {
                p=-1;
                break;
            }
            inceput = p;
        }
        if (inceput == capat){
            p=-1;
            break;
        }
    }
    if (n != 0)
    fo <<p;
    else fo <<1;
    fu.close();
    fo.close();
}