#include <fstream>
#define lim 2400000

using namespace std;

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

unsigned P;

unsigned function(unsigned val)
{
    return val / 5 + val / 25 + val / 125 + val / 625 + val / 3125 + val / 15625 + val / 78125 + val / 390625 + val / 1953125 + val / 9765625 + val / 48828125 + val / 244140625;
}

int main()
{
    in >> P;
    if(P > lim)
    {
        out << -1;
        return 0;
    }
    for(unsigned k = 1; ; ++k)
        if(function(k) == P)
        {
            out << k;
            break;
        }
    return 0;
}