#include <iostream>
#include <fstream>
using namespace std;

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

int main()
{
   int p, nr2=0, nr5=0, nr=0, k=2, min1, x ;
    f>>p;
   while (nr<p)
   {x=k;
   while(x%2==0)
              {nr2++;
               x/=2;}
   while (x%5==0)
                   {nr5++;
                    x/=5;}
   if (nr2<nr5) min1=nr2;
        else min1=nr5;
   nr=nr+min1;
   nr5=nr5-min1;
   nr2=nr2-min1;
   k++;
   }

  if (nr=p)
        g<<--k;
    else g<<"-1";

    return 0;
}