#include<bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
typedef pair<pii, int> ppi;
map<pii, int> m;
int a, b, c, d;
ppi p(int i, int j, int k) {
return ppi(pii(i, j), k);
}
void solve() {
queue<ppi> q;
q.push(p(0, 0, 0));
while(q.size() != 0) {
ppi t = q.front();
q.pop();
int i = t.first.first, j = t.first.second, k = t.second;
m.insert(p(i, j, k));
if(m.insert(p(0, j, k+1)).second) q.push(p(0, j, k+1));
if(m.insert(p(i, 0, k+1)).second) q.push(p(i, 0, k+1));
if(m.insert(p(a, j, k+1)).second) q.push(p(a, j, k+1));
if(m.insert(p(i, b, k+1)).second) q.push(p(i, b, k+1));
int u = min(b-j, i);
if(m.insert(p(i-u, j+u, k+1)).second) q.push(p(i-u, j+u, k+1));
u = min(a-i, j);
if(m.insert(p(i+u, j-u, k+1)).second) q.push(p(i+u, j-u, k+1));
}
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
cin >> a >> b >> c >> d;
solve();
int r = m.find(pii(c, d))->second;
if(r) cout << r;
else cout << -1;
return 0;
}
