Up and Down

#include <iostream>
#include <queue>
#include <vector>
#include <cstring>

using namespace std;

int main() {
    while (true) {
        int N, A, B;
        cin >> N;
        if (N == 0) break;

        cin >> A >> B;

        vector<int> K(N + 1);  // Floor indices from 1 to N
        for (int i = 1; i <= N; ++i) {
            cin >> K[i];
        }

        vector<int> visited(N + 1, -1);  // visited[i] = number of presses to reach floor i
        queue<int> q;

        q.push(A);
        visited[A] = 0;

        while (!q.empty()) {
            int current = q.front();
            q.pop();

            if (current == B) break;

            int up = current + K[current];
            int down = current - K[current];

            if (up <= N && visited[up] == -1) {
                visited[up] = visited[current] + 1;
                q.push(up);
            }

            if (down >= 1 && visited[down] == -1) {
                visited[down] = visited[current] + 1;
                q.push(down);
            }
        }

        cout << visited[B] << endl;
    }

    return 0;
}