#pragma GCC optimize("O2")
#pragma GCC target("avx,avx2,fma")
//----------Huuuu------
#include <bits/stdc++.h>
using namespace std;
//-----------Define---------------
#define __File(name)
/*   freopen(name ".inp", "r", stdin);
    freopen(name ".out", "w", stdout); */
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
#define el cout << '\n'
#define ll long long
#define ull unsigned long long
#define big __int128
#define gcd(a, b) abs(__gcd(a, b))
#define lcm(a, b) abs((a) * (b) / gcd(a, b))
#define fix(a, b) fixed << setprecision(a) << (b)
#define all(x) (x).begin(), (x).end()
#define all1(x) (x) + (1), (x) + (n) + (1)
#define rep(i, a, b) for (int i = a; i < b; i++)
#define rep1(i, a, b) for (int i = a; i <= b; i++)
#define out(x)
#define pb push_back
#define pob pop_back()
#define fi first
#define se second
/*   __File("t.phistdeptrai");*/
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int s1, v1, s2, v2;
    cin >> s1 >> v1 >> s2 >> v2;

    if (v1 == v2)
    {
        if (s1 == s2)
        {
            cout << 0 << endl;
        }
        else
        {
            cout << -1 << endl;
        }
    }
    else
    {
        int t = int(s2 - s1) / (v1 - v2);
        if (t > 0)
        {
            cout << t << endl;
        }
        else
        {
            cout << -1 << endl;
        }
    }

    return 0;
}