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

ifstream in("fact.in");
ofstream out("fact.out");
int nrzerouri(int nr){
    int z = nr / 5;
    int zeros = z;
    while (z >= 5){
        z = z / 5;
        zeros += z;
    }
    return zeros;
}

int main(){
    int p;
    in >> p;
    int nr = p*5;
    int k = nrzerouri(nr);
    int diff = k - p;
    while (diff != 0){
        nr -= (diff) * 5;
        k = nrzerouri(nr);
        if (diff * (k - p) == -1){
            nr = -1;
            break;
        }
        diff = k-p;
    }
    out << nr;
}