#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int INF=2147483647;
int inf=-2147483648;
int mod=1000000007;
#define read(x) cin >> x;
#define fo(i,n) for(i=0;i<n;i++)
#define one(x) cout<<(x)<<endl;
#define two(a,b) cout<<(a)<<" "<<(b)<<endl;
#define three(a,b,c) cout<<(a)<<" "<<(b)<<" "<<(c)<<endl;
#define four(a,b,c,d) cout<<(a)<<" "<<(b)<<" "<<(c)<<" "<<(d)<<endl;
#define write(a,i) cout << a[i] << " ";
map <int,bool> m;
int main()
{
    int a,b,c,d,kol=0;
    cin >> a >> b >> c >> d;
    while (1)
    {
        m[b]=1;b+=a;
        if (kol>100000) break;
        kol++;
    }
    kol=0;
    while (1)
    {
        if (m[d]==1)
        {
            cout << d;
            return 0;
        }
        d+=c;
        if (kol>100000)
        {
            cout << -1;
            return 0;
        }
        kol++;
    }
    return 0;
}