//
// Created by dragos on 28.01.2019.
//

#include <iostream>
#include <fstream>

using namespace std;

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

int p;
int main() {

    fin>>p;

    if(p == 0) {
        fout<<1;
    } else {
        int sol = 5 * p;
        int err = 5;
        int k = 0;
        while(err * 5 < sol) {
            k++;
            err*=5;
        }

        if(err * 5 == sol) {
            fout<< -1;
        } else {
            sol -= (k*(k+1))/2 * 5;
            fout<<sol;
        }
    }

    fin.close();
    fout.close();

    return 0;
}