#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    int p,cnt=0,cnt2=0,i=1;
    long long f = 1, cf;
    in >> p;
    if(p <= 4)
    {
        for(int i = 1; i <= 20; i++)
        {
          cnt = 0;
          f = f * i;
          cnt2++;
          cf = f;
          while(cf > 0)
          {
            if(cf % 10 == 0)
              cnt++;
            else
              break;
            cf /= 10;
          }
          if(cnt >= p)
            break;
        }
        out << cnt2;
    }
    else
    {
        out << -1;
    }
    return 0;
}