function Main(input) {
  input = input.split(" ");
  const n = Number(input[0])
  const a = Number(input[1])
  const b = Number(input[2])
  
  if(n < 2) {
    return console.log(0)
  }
  
  const combinations = []
  for(var i = 1; i <= n; i++) {
    if(i !== a && i !== b) {
  		combinations.push(getCombination(n, i))
    }
  }
  const result = combinations.reduce((a, b) => a * b)
  console.log(result)
}

function getCombination(total, choose){
  // 分子
  var numerator = total
  for(var i = 1; i < choose; i++){
    numerator = numerator * (total - i)
  }
  // 分母
  const denominator = factorialize(choose)
  return numerator / denominator
}

function factorialize(k) {
  if(k <= 1){
    return 1;
  }
  return k * factorialize(k - 1);
}
 
Main(require("fs").readFileSync("/dev/stdin", "utf8"));