def main():
    x_dst, y_dst = list(map(
        int, input().split()
    ))

    x_fu, y_fu = list(map(
        int, input().split()
    ))

    # ゴールが対角線上かつ，その通り道に歩がいる場合のみ
    # 1回無駄な動きが生じる
    move = 0
    if x_dst == y_dst:
        if x_dst > 0 and y_dst > 0 and x_fu > 0 and y_fu > 0 and x_fu == y_fu and x_dst > x_fu:
            move += 1

        if x_dst < 0 and y_dst > 0 and x_fu < 0 and y_fu > 0 and x_fu == y_fu and x_dst < x_fu:
            move += 1

        if x_dst < 0 and y_dst < 0 and x_fu < 0 and y_fu < 0 and x_fu == y_fu and x_dst < x_fu:
            move += 1

        if x_dst > 0 and y_dst < 0 and x_fu > 0 and y_fu < 0 and x_fu == y_fu and x_dst > x_fu:
            move += 1

        move += x_dst
        print(move)

    else:
        x_dst_abs, y_dst_abs = abs(x_dst), abs(y_dst)

        bigger = max(x_dst_abs, y_dst_abs)
        smaller = min(x_dst_abs, y_dst_abs)

        move = (bigger - smaller) + smaller
        print(move)

main()