//This DJ program inputs a natural number n 
//and then outputs n factorial, which is
//calculated in a recursive function

class Factorial extends Object {
  //  Returns n!   
  nat factorial(nat n) {
    if(n>1) {n*factorial(n-1);}
    else {1;};
  }
}

main {
  var Factorial f;
  f = new Factorial;
  printNat(f.factorial(readNat()));
}