#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    while(b<=10000000){
        if(b>d)d+=c;
        if(b<d)b+=a;
        if(b==d){
            cout<<b;
            return 0;
        }
    }
    cout<<-1;
}