#include<bits/stdc++.h>
#include<atcoder/all>
#define chmin(x,y) (x) = min((x),(y))
#define chmax(x,y) (x) = max((x),(y))
#define ld long double
using namespace std;
using namespace atcoder;
using ll = long long;
const ll mod = 998244353;
using mint = modint998244353;
using Graph = vector<vector<int>>;
const vector<int> dx = {1,0,-1,0}, dy = {0,1,0,-1};

int main(){
  // input
  int A,B,a,b; cin >> A >> B >> a >> b;
  for(int i = 0; i < B; i++){
    int C = A * i + a;
    if(C % B == b){
      cout << C << endl;
      break;
    }
  }
}