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