use proconio::input;

const MAX: u128 = u128::pow(10, 9) + 7;

fn main() {
    input!{
        h: u128,
        w: u128,
        a: u128,
        b: u128,
    };

    // Ok it seems like this way is too naive for this problem and I actually have
    // to do some magic with combinations or something else I haven't even thought of

    // But I don't think you can do combinations because you need to divide big numbers
    // and you can't do that with modulo iirc

    let mut dp = vec![vec![0; w as usize]; h as usize];
    for i in 0..(h-a) {
        dp[i as usize][0] = 1;
    }
    for j in 0..w {
        dp[0][j as usize] = 1;
    }

    for i in 1..h {
        for j in 1..w {
            if !(i >= h - a && j < b) {
                dp[i as usize][j as usize] = (dp[(i - 1) as usize][j as usize] + dp[i as usize][(j - 1) as usize]) % MAX;
            }
        }
    }

    // for row in &dp {
    //     for cell in row {
    //         print!("{} ", {cell});
    //     }
    //     print!("\n");
    // }

    println!("{}", {dp[(h-1) as usize][(w-1) as usize]});
}