#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int P,n,x,i,nr5;
int main()
{
   f>>P;
   n=0;
   if(P==0)
   g<<1;
   else {

   while(nr5!=P)
   {
       ++n;
       nr5=0;
      for(i=1;i<=n;++i)
      {
          x=i;
          while(x%5==0)
          {
              nr5++;
              x=x/5;
          }
      }
   }
   g<<n;
   }

    return 0;
}