#include "bits/stdc++.h"

using namespace std;

long zero ( long a)
{
    long s = 0;
    long b = 5;
    while (a >= b) {
        s += a/b;
        b *= 5;
    }
    return s;
}

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");

    long p;
    cin >> p;
    long c = 1;
    while (zero(c) < p) {
        c++;
    }
    if (zero(c) != p) {
        cout << -1;
    }
    else
        cout << c;
    return 0;
}