#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i, m, n) for (ll i = m; i < n; i++)
#define rrep(i, m, n) for (ll i = m - 1; i >= n; i--)
#define pb(n) push_back(n)
#define UE(N) N.erase(unique(N.begin(), N.end()), N.end());
#define Sort(n) sort(n.begin(), n.end())
#define Rev(n) reverse(n.begin(), n.end())
#define HOUT(S) cout << setprecision(50) << S << endl
#define pint pair<ll, ll>
#define paf(L, R) pair<L, R>
#define mod 998244353
#define MAX 10000010
#define endl "\n"
#define ALL(a) a.begin(), a.end()
#define chmax(a, b) a = (((a) < (b)) ? (b) : (a))
#define chmin(a, b) a = (((a) > (b)) ? (b) : (a))

template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value != 0>::type fill_v(U& u, const V... v) {
    u = U(v...);
}

template <typename T, typename U, typename... V>
typename enable_if<is_same<T, U>::value == 0>::type fill_v(U& u, const V... v) {
    for (auto& e : u) fill_v<T>(e, v...);
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll A, B, N, M;
    cin >> A >> B >> N >> M;
    if(A > B) {
        ll x = (A - B) / N + 10;
        while(x * N + B + x > A) x--;
        cout << x + B << endl;
    }
    else {
        ll x = (B - A) / M + 10;
        while(x * M + A + x > B) x--;
        cout << x + A << endl;
    }
}