#include <iostream>
#include <fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");
long long Zr(int x)
{
    long long p  = 5, nr = 0;
    while(x >= p)
    {
        nr += x/p;
        p *= 5;
    }
    return nr;
}
int main()
{
   long long p, m, st, dr;
   in >> p;
   if(p == 0)out << 1 << "\n";
   else
   {
       st = 1;
       dr = p * 5 + 100;
       while(st <= dr)
       {
           m = (st + dr)/2;
           if(Zr(m) >= p)dr = m - 1;
           else st = m + 1;
       }
       if(Zr(st) == p)out << st << "\n";
       else out << -1;
   }
    return 0;
}