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

ifstream fin("fact.in");
ofstream fout("fact.out");
int p, n;

int nr0(int n) {
    if (n < 0) return -1;
    else {
        int k = 0;
        for (int i = 5; n/i >= 1; i *= 5)
            k += n/i;
        return k;
    }
}

int main() {
    fin >> p;
    if (p < 0)
        fout << -1;
    else
        for (int i = 1; i <= 10e8; ++i)
            if (nr0(i) == p) {
                fout << i;
                break;
            }
    return 0;
}