public void Solve()
{
var max = Math.Max(A, B);
Modular[] dp = new Modular[max + 1];
dp[1] = N;
for (int i = 1; i < max; i++)
{
dp[i + 1] = dp[i] * (N - i) / (i + 1);
}
var all = Modular.Pow(2, (int)N);
Console.WriteLine((int)(all - dp[A] - dp[B] - 1));
}
public static Modular Pow(Modular a, int n)
{
switch (n)
{
case 0:
return(1);
case 1:
return(a);
default:
var p = Pow(a, n / 2);
return(p * p * Pow(a, n % 2));
}
}