#include<fstream.h>

typedef struct
{
  int d2, d5;
} exponent;

int n, nr;
exponent x;

void citire()
{
  ifstream in("fact.in");
  in>>n;
  in.close();
}



exponent nr_exp(int a)
{
  int i, j;
  x.d2=x.d5=0;
  for (j=1; j<=a; j++)
    {

	  i=j;
	  while (i%2==0)
	    {
	      x.d2++;
	      i/=2;
	    }
	  while (i%5==0)
	    {
	      x.d5++;
	      i/=5;
	    }
    }
  return x;
}

int main()
{
  citire();
  exponent manevra;
  int ok=1;
  while (ok)
    {
      nr++;
      manevra=nr_exp(nr);
      if (manevra.d2>=n && manevra.d5>=n) ok=0;
    }
  ofstream out("fact.out");
  out<<nr;
  out.close();
  return 0;
}