#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef tuple<int, int, int> tii;
typedef vector<int> vi;

#define eb emplace_back
#define all(s) (s).begin(), (s).end()
#define rep(i, a, b) for (int i = (a); i <= (b); ++i)
#define per(i, a, b) for (int i = (a); i >= (b); --i)

inline int rd() {
    int x = 0;
    bool f = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) f |= (c == '-');
    for (; isdigit(c); c = getchar()) x = x * 10 + (c ^ 48);
    return f ? -x : x;
}

constexpr int N = 107;
constexpr int inf = INT_MAX;

bool vis[N][N];

int n, m, p, q, dp[N][N];

bool valid(int x, int y) {return !x || (x + q >= y);}

void dfs(int X, int Y) {
    if (vis[X][Y]) return;
    int x[2] = {X, n - X};
    int y[2] = {Y, m - Y};
    vis[X][Y] = true;
    if (X <= p) {dp[X][Y] = 1; return;}
    if (!valid(x[1], y[1])) {dp[X][Y] = -1; return;}
    int res = inf;
    rep(i, 0, min(p, x[0]))
        rep(j, 0, min(p - i, y[0])) if (i + j > 0 && valid(x[0] - i, y[0] - j)) {
            rep(j2, 0, min({p, x[1] + j, i + j - 1})) {
                int nx = x[0] - i, ny = y[0] - j + j2;
                dfs(nx, ny);
                if (dp[nx][ny] != -1) res = min(res, dp[nx][ny]);
            }
        }
    if (res == inf) res = -1;
    else res += 2;
    dp[X][Y] = res;
}

int main() {
    n = rd(), m = rd();
    p = rd(), q = rd();
    dfs(n, m);
    printf("%d\n", dp[n][m]);
    return 0;
}