#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int putere5(int a)
{ int result=0;
  uint64_t p5=5;
  while(p5<=a)
  { result+=a/p5;
    p5*=5;
  }
  return result;
}

int main()
{ int n;
  fin>>n;
  if(!n) fout<<"1";
  else
  { int i=4*n;
    int p5=putere5(i);
    while(p5!=n)
    { i+=5;
    }
   fout<<i;
  }


    return 0;
}