#include <iostream>
using namespace std;
int happyPeople(int Num1, int Num2, int X, int Y) {
int i = 1;
int countA = 0;
int countB = 0;
while (true) {
if (countA < Num1 && i % X != 0) countA++;
if (countB < Num2 && i % Y != 0) countB++;
if (countA >= Num1 && countB >= Num2) return i;
i++;
}
}
int main() {
int Num1, Num2, X, Y;
cin >> Num1 >> Num2 >> X >> Y;
cout << happyPeople(Num1, Num2, X, Y);
return 0;
}
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