"use strict";
const factorial = num => {
  let number = 1;
  for (let i = 1; i <= num; i++) {
    number *= i;
  }
  return number;
};
function Main(input) {
  input = input.split(" ").map(Number);
  let total = 0;
  for (let i = 1; i <= input[0]; i++) {
    if (input[1] === i || input[2] === i) continue;
    total += factorial(input[0]) / (factorial(i) * factorial(input[0] - i));
  }
  console.log(total % (Math.pow(10, 9) + 7));
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));