include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

typedef long long lint;

const int N=100*1000;

lint n;
lint a, b, c, d;
lint mas[110];
bool r=false;

int main() {
    cin>>a>>b>>c>>d;
    if(b<d) {
        swap(a, c);
        swap(b, d);
    }
    for(n=0; n<=max(b, d)+c; n++) {
        if((b%c+(a%c)*(n%c))%c==d%c ) {
            r=true;
            break;
        }
        //if(mas[n%c]==0) mas[n%c]++;
        //else break;
    }
    if(r) cout<<b+a*n<<endl;
    else cout<<-1<<endl;


    return 0;