#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    fstream f("factorial.in", ios::in);
    fstream g("factorial.out", ios::out);

    int p, n = 0, x;

    f>>p;
    while(p > 0)
    {
        x = 0;
        n += 5;
        for(int r = n; r % 5 == 0; r /= 5)
            ++x;
        p -= x;
    }

    if(p == 0)
        g << n;
    else
        g << -1;
    return 0;
}