#55669: c++ bfs
#include <bits/stdc++.h>
using namespace std;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int n, p, l, r;
if (!(cin >> n >> p >> l >> r)) return 0;
vector<int> v(n);
for(int i = 0; i < n; i++) cin >> v[i];
vector<int> step(n, -1);
queue<int> q;
q.push(0);
step[0] = 0;
int ans = -1;
while(!q.empty()){
int curr = q.front();
q.pop();
if (curr == p) {
ans = step[curr];
break;
}
int next_positions[2] = {curr - l, curr + r};
for (int next_pos : next_positions) {
if (next_pos < 0 || next_pos >= n) continue;
int target = v[next_pos];
if (target < 0 || target >= n) continue;
if (step[target] == -1) {
step[target] = step[curr] + 1;
q.push(target);
}
}
}
cout << ans << "\n";
return 0;
}