#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<cmath>
#include<queue>
#include<stack>
#include<map>
#include<set>

using namespace std;
typedef long long ll;
#define loop1(n) for(int loopt = 0; loopt < (n); loopt++)
#define loop2(i,n) for((i) = 0; (i) < (n); (i)++)
#define loop3(i,k,n) for((i) = (k); (i) < (n); (i)++)
#define GET_NAME_LOOP(_2,_3,NAME,...) NAME
#define loop(n,...) GET_NAME_LOOP(__VA_ARGS__,loop3,loop2,loop1)(n,__VA_ARGS__)

#define rloop1(n) for(int loopt = (n)-1; loopt >= 0; loopt--)
#define rloop2(i,n) for((i) = (n)-1; (i) >= 0; (i)--)
#define rloop3(i,k,n) for((i) = (k)-1; (i) >= (n); (i)--)
#define GET_NAME_RLOOP(_2,_3,NAME,...) NAME
#define rloop(n,...) GET_NAME_RLOOP(__VA_ARGS__,rloop3,rloop2,rloop1)(n,__VA_ARGS__)

#define outone cout << "First" << endl
#define outtwo cout << "Second" << endl
#define outyes cout << "Yes" << endl
#define outno cout << "No" << endl
#define outans cout << ans << endl
#define all(i) i.begin(),i.end()
//const ll mod =  998244353L;
//const ll mod = 1e9+7L;
//const double PI =3.14159265359d;
//const double E =2.718281828d;

int main() {
    int i,j,k;
    ll A,B,a,b;
    cin >> A >> B >> a >> b;
    while(a != b){
        if(a > b) b+=B*(((a-b-1)/B)+1);
        else a+=A*(((b-a-1)/A)+1);
    }
    cout << a;
}