#include <fstream>
using namespace std;
int calc(int n)
{ int s=0;
  while(n%5==0)
  { s++;
    n=n/5;
  }
  return s;
}
int main()
{ ifstream in("fact.in");
  ofstream out("fact.out");
  int p,i,s=0;
  in>>p;
  if(p==0)
  {out<<"1"; return 0;}
  i=0;
  while(s<=p)
  { i=i+5;
    s=s+calc(i);
  }
  out<<i-5;
    return 0;
}