#include <bits/stdc++.h>

#define f first
#define s second
#define pb push_back
#define mp make_pair

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int N = 300500, inf = 1e9, mod = 998244353;
const ll INF = 1e18;

int sum(int a, int b) {
    a += b;
    if (a >= mod)
        a -= mod;
    return a;
}

int sub(int a, int b) {
    a -= b;
    if (a < 0)
        a += mod;
    return a;
}

int mult(int a, int b) {
    return 1ll * a * b % mod;
}

int bp(int a, int b) {
    int res = 1;
    while (b) {
        if (b & 1)
            res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

int inv(int x) {
    return bp(x, mod - 2);
}

void solve() {
    vector<int> a(4);
    for (int i=0;i<4;i++) cin >> a[i];
    a[0] = (a[1]-a[0])%a[1];
    a[2] = (a[3]-a[2])%a[3];
    for (int b=0;b<100;b++)
    {
        int x = a[1]*b+a[0];
        if (x%a[3]!=a[2]) continue;
        cout << x << "\n";
        return;
    }
}

int main() {
//#ifdef DEBUG
//    freopen("input.txt", "r", stdin);
//#endif
    ios_base::sync_with_stdio(false);
    int t = 1;
//    cin >> t;
    for (int i = 1; i <= t; i++) {
//        cout << "Case #" << i << endl;
        solve();
    }
}