#include <bits/stdc++.h>   using namespace std;   int sum[100005];   int main() {     int h1, h2, a, b, k, x;     cin >> h1 >> h2 >> a >> b;     int num = h1 + a * 8;     if (num >= h2)       x = 0;     else if (a <= b)       x = -1;     else {       x = 1;       num -= b * 12;       for (int i = 1;; i++) {         num += a * 12;         if (num >= h2)           break;         else {           x++;           num -= b * 12;         }       }     }     cout << x << endl;     return 0;   }   