#include<stdio.h>

int main(void) {
	long long int A, B, N, M;
	scanf("%lld %lld %lld %lld", &A, &B, &N, &M);
	if (A > B) {
		while (A - N > B + 1) {
			A -= N;
			B++;
		}
		printf("%lld", B);
	}else{
		while (B - M > A + 1) {
			B -= M;
			A++;
		}
		printf("%lld", A);
	}
}