#include <bits/stdc++.h>
// #include <atcoder/all>
using namespace std;

#define lli long long int
#define REP(i, s, n) for (lli i = s; i < n; i++)
#define INF (1LL << 62)
#define DEBUG 0
#define mp(a, b) make_pair(a, b)
#define SORT(V) sort(V.begin(), V.end())
#define PI (3.141592653589794)
#define TO_STRING(VariableName) #VariableName
#define LOG1(x) \
    if (DEBUG) cout << TO_STRING(x) << "=" << x << " " << endl;
#define LOG2(x, y)                                                          \
    if (DEBUG)                                                              \
        cout << TO_STRING(x) << "=" << x << " " << TO_STRING(y) << "=" << y \
             << endl;
#define LOG3(x, y, z)                                                       \
    if (DEBUG)                                                              \
        cout << TO_STRING(x) << "=" << x << " " << TO_STRING(y) << "=" << y \
             << " " << TO_STRING(z) << "=" << z << endl;
#define LOG4(w, x, y, z)                                                      \
    if (DEBUG)                                                                \
        cout << TO_STRING(w) << "=" << w << " " << TO_STRING(x) << "=" << x   \
             << " " << TO_STRING(y) << "=" << y << " " << TO_STRING(z) << "=" \
             << z << endl;
#define LOG5(w, x, y, z, a)                                                   \
    if (DEBUG)                                                                \
        cout << TO_STRING(w) << "=" << w << " " << TO_STRING(x) << "=" << x   \
             << " " << TO_STRING(y) << "=" << y << " " << TO_STRING(z) << "=" \
             << z << " " << TO_STRING(a) << "=" << a << endl;
#define LOG6(w, x, y, z, a, b)                                                \
    if (DEBUG)                                                                \
        cout << TO_STRING(w) << "=" << w << " " << TO_STRING(x) << "=" << x   \
             << " " << TO_STRING(y) << "=" << y << " " << TO_STRING(z) << "=" \
             << z << " " << TO_STRING(a) << "=" << a << " " << TO_STRING(b)   \
             << "=" << b << endl;

#define overload6(a, b, c, d, e, f, g, ...) g
#define LOG(...) \
    overload6(__VA_ARGS__, LOG6, LOG5, LOG4, LOG3, LOG2, LOG1)(__VA_ARGS__)

template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}

mt19937 engine;
std::chrono::system_clock::time_point start, endTime;

std::ostream &operator<<(std::ostream &dest, __int128_t value) {
    std::ostream::sentry s(dest);
    if (s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
            --d;
            *d = "0123456789"[tmp % 10];
            tmp /= 10;
        } while (tmp != 0);
        if (value < 0) {
            --d;
            *d = '-';
        }
        int len = std::end(buffer) - d;
        if (dest.rdbuf()->sputn(d, len) != len) {
            dest.setstate(std::ios_base::badbit);
        }
    }
    return dest;
}

__int128 parse(string &s) {
    __int128 ret = 0;
    for (int i = 0; i < s.length(); i++) {
        if ('0' <= s[i] && s[i] <= '9') {
            ret = 10 * ret + s[i] - '0';
        }
    }
    return ret;
}

lli gcd(lli a, lli b) {
    if (a == 0) return b;
    if (b == 0) return a;
    if (a % b == 0) {
        return b;
    } else {
        return gcd(b, a % b);
    }
}
void solve() {
    lli A, B, a, b;
    cin >> A >> B >> a >> b;

    REP(x, 0, 100000000) {
        if (x % A == a && x % B == b) {
            cout << x << endl;
            return;
        }
    }
}

// Generated by 2.12.0 https://github.com/kyuridenamida/atcoder-tools  (tips:
// You use the default template now. You can remove this line by using your
// custom template)
int main() {
    lli n = 1;
    // cin>>n;
    while (n--) solve();
    return 0;
}

struct Setup {
    Setup() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
    }
} __Setup;