use std::io::*;
//use std::num;
use std::str::FromStr;
//use std::time::Instant;

fn main() {
    //let now = Instant::now();
    let a: isize = read();
    let b: isize = read();
    let c: isize = read();
    let d: isize = read();
    let mut flag = 0;

    let mut x = -100;
    loop {

        if x == 100 {
            break;
        }
        
        let mut y = -100;
        loop {            
            if y == 100 {
                break;
            }
            if b + a * x == d + c * y && b + a * x >= 0 {
                flag = 1;

                println!("{}", b + a * x);
                break;
            }
            y += 1;
        }
        if flag == 1 {
            break;
        }
        x += 1;
    }

    if flag == 0 {
        println!("NaN");
    }

    //println!("[DEBUG_PRINT] {} ms", now.elapsed().as_millis());
}

pub fn min(x: usize, y: usize) -> usize {
    let z: usize;

    if x <= y {
        z = x;
    } else {
        z = y;
    }

    return z;
}

pub fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

pub fn read_array() -> Vec<char> {
    let array: String = read();
    let chars: Vec<char> = array.trim().chars().collect::<Vec<char>>();
    chars
}

pub fn get_data() -> Vec<u64> {
    let mut s: String = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let vec: Vec<u64> = s
        .trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect();

    vec
}

pub fn get_chars() -> Vec<char> {
    let mut s: String = String::new();
    std::io::stdin().read_line(&mut s).ok();

    let vec: Vec<char> = s.trim().chars().collect::<Vec<char>>();

    vec
}