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

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

int nrZerouriFact(int x)
{
    int s = 0;
    while (x > 0){
        s += x / 5;
        x /= 5;
    }
    return s;
}


int main()
{
    int p, stanga, dreapta, sol;
    fin >> p;
    stanga = 1, dreapta = 1000000000;
    while (stanga <= dreapta){
        int mijloc = (stanga + dreapta) / 2;
        if (nrZerouriFact(mijloc) >= p){
            sol = mijloc;
            dreapta = mijloc - 1;
        }
        else
            stanga = mijloc + 1;
    }
    if (nrZerouriFact(sol) == p)
        fout << sol;
    else
        fout << -1;
    return 0;
}