#include<bits/stdc++.h>
using namespace std;
//------------------
#define ll long long
#define int long long
#define dcchuyentoan ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define el cout << endl
//------------------
ll a,b,c,d;
//------------------
signed main()
{
    dcchuyentoan;
    
    cin >> a >> b >> c >> d;
    
    if(c == d)
    {
        if(a == c)
        {
            cout << 0;
        }
        else
        {
            cout << -1;
        }
    }
    else
    {
        ll x = c - a;
        ll y = b - d;
        
        if(y == 0 || x % y != 0)
        {
            cout << -1;
        }
        else
        {
            if (x / y < 0)
            {
                cout << -1;
            }
            else
            {
                cout << (x / y);
            }
        }
    }
}

$\dcchuyentoan$