#include<bits/stdc++.h>
using namespace std;
#define ll long long int
int main()
{
    ll a,b,c,d;
    cin>>a>>b>>c>>d;
    if(b==d)
    {
        cout<<b<<endl;
        return 0;
    }
    ll ara[10000],ara2[10000];
    ll i=0;
    bool flag=false;
    bool flag2=false;
    if(b%2==0)ara[i]=1;
    else ara[i]=0;
    i++;
    ll j=0;
    if(d%2==0)ara2[j]=1;
    else ara2[j]=0;
    j++;
    while(1)
    {
        if(b<d)
        {
            b+=a;
            //a+=a;
            if(b%2==0)ara[i]=1;
            else ara[i]=0;
            if(ara[i]!=ara[i-1])flag=true;
            i++;
        }
        else
        {
            d+=c;
            //c+=c;
            if(d%2==0)ara2[j]=1;
            else ara2[j]=0;
            if(ara2[j]!=ara2[j-1])flag2=true;
            j++;
        }
        if(b==d)
        {
            cout<<b<<endl;
            break;
        }
        if(i>10&&j>10)
        {
            if(flag==false&&flag2==false&&ara[0]!=ara2[0])
            {
                cout<<"-1"<<endl;
                return 0;
            }
            else continue;
        }
        //cout<<b<<" "<<d<<endl;
    }
    return 0;
}