let val = new Int32Array(200010);
let idx = 0;
let next = new Int32Array(200010);
let head = new Int32Array(100010).fill(-1);

let add = (a, b) => {
    val[idx] = b;
    next[idx] = head[a];
    head[a] = idx++;
}

let used = new Int32Array(100010);
let bfs = (x, y) => {
    let queue = [x];
    let step = -1;
    while (queue.length > 0) {
        step++;
        let nextStep = [];
        for (let i = 0; i < queue.length; i++) {
            used[queue[i]] = 1;
            if(queue[i] === y) return step;
            for (let j = head[queue[i]]; j != -1; j = next[j]) {
               if (!used[val[j]]) nextStep.push(val[j]);
            }
        }
        queue = nextStep;
    }
    return -1;
}


let buf = '';
process.stdin.on('readable', function () {
    let chunk = process.stdin.read();
    if (chunk) buf += chunk.toString();
});
let getInputNums = line => line.split(' ').filter(s => s !== '').map(x => parseInt(x));
let getInputStr = line => line.split(' ').filter(s => s !== '');
process.stdin.on('end', function () {
    let n = 0, m = 0;
    buf.split('\n').forEach(function (line, lineIdx) {
        if (lineIdx === 0) {
            n = getInputNums(line)[0];
            m = getInputNums(line)[1];
        } else {
            let arr = getInputNums(line);
            add(arr[0], arr[1]);
            if (lineIdx === m) {
                console.log(bfs(1, n));
            }
        }
    });
});