import * as fs from "fs"

const bitCount = (n: number): number => {
    n = n - ((n >>> 1) & 0x55555555)
    n = (n & 0x33333333) + ((n >>> 2) & 0x33333333)
    n = (n + (n >>> 4)) & 0x0f0f0f0f
    n = n + (n >>> 8)
    n = n + (n >>> 16)
    return n & 0x3f
}

const calcDist = (a: number, b: number): number => {
    return bitCount(a ^ b)
}

const bfs = (n: number, arr: number[]): number => {
    const que: number[] = [0]
    const dist = Array(n).fill(-1)
    dist[0] = 0

    while (que.length !== 0) {
        const v = que.shift()
        for (let u = 0; u < n; u++) {
            if (dist[u] !== -1) continue
            if (calcDist(arr[v], arr[u]) !== 1) continue
            dist[u] = dist[v] + 1
            que.push(u)
        }
    }
    return dist[n - 1]
}

const main = (args: string): void => {
    const input = args.trim().split("\n");
    const N = +input.shift()
    const [start, end] = input.shift().split(" ").map(x => Number(x))
    let stones = [start]
    stones = stones.concat(input.shift().split(" ").map(x => Number(x)))
    stones.push(end)

    const ans: number = bfs(N + 2, stones);
    console.log(ans === -1 ? ans : ans - 1)
}

main(fs.readFileSync('/dev/stdin', 'utf8'));