2. Такси

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        int ans = a;
        if (a >= c) {
            System.out.println(a);
            return;
        }
        while (true) {
            if (a + b <= c) {
                ans = a + b;
                a += b;
            } else {
                ans = c;
                break;
            }
            if (c - d >= a) {
                ans = c - d;
                c -= d;
            } else {
                ans = a;
                break;
            }
        }
        System.out.println(ans);
    }
}