#include <cctype>
#include <string>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <bits/stdc++.h>
#include <atcoder/all>
#include <math.h>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
using namespace atcoder;
using ll = long long;
using p = pair<int,int>;
using mod = modint998244353;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

vector<pair<char,int>> RunLength(string s){
    vector<pair<char,int>> R;
    int n = s.size();
    int pre = 0;
    rep(i,n - 1){
        if(s[i + 1] != s[i]){
            R.push_back({s[i],i - pre + 1});
            pre = i + 1;
        }
    }
    if(pre != n)R.push_back({s[n - 1],n - pre});
    return R;
}

int op(int a,int b){return min(a,b);}
int e(){return (int)1e9;}
segtree<int,op,e> seg(1);

int main(){
    int n,m,a,b,c;
    string s,t;
    int A,B;cin >> A >> B >> a >> b;
    for(int x = 0;x < 1e7;x++){
        if(x%A == a && x%B == b){
            cout << x << endl;
            return 0;
        }
    }
}