use std::io;

fn main() {
    let mut line = String::new();
    io::stdin().read_line(&mut line).unwrap();
    let mut tokens = line.trim_end().split_whitespace().map(|v| v.parse::<usize>().unwrap());
    let A = tokens.next().unwrap();
    let B = tokens.next().unwrap();
    let a = tokens.next().unwrap();
    let b = tokens.next().unwrap();

    for y in 0.. {
        let x = y*A + a;
        if x%B == b {
            println!("{}", x);
            break
        }
    }
}