#!/usr/bin/python3

import bisect
import collections
import heapq
import itertools
import math
import os
import sys


def main():
    A, B, a, b = read_ints()
    if A < B:
        A, B, a, b = B, A, b, a
    x = a
    while True:
        if x % B == b:
            print(x)
            break
        x += A


###############################################################################

DEBUG = 'DEBUG' in os.environ


def inp():
    return sys.stdin.readline().rstrip()


def read_int():
    return int(inp())


def read_ints():
    return [int(e) for e in inp().split()]


def list2d(d1, d2, init=None):
    return [[init] * d2 for _ in range(d1)]


def list3d(d1, d2, d3, init=None):
    return [[[init] * d3 for _ in range(d2)] for _ in range(d1)]


def list4d(d1, d2, d3, d4, init=None):
    return [[[[init] * d4 for _ in range(d3)] for _ in range(d2)]
            for _ in range(d1)]


def debug(fmt, *args):
    if DEBUG:
        if args:
            print(fmt.format(*args), file=sys.stderr)
        else:
            print(fmt, file=sys.stderr)


if __name__ == '__main__':
    main()