function sockMerchant(n, ar) {
    let res = 0;
    let a = 0;
    for (; a < n; a++) {
        let b = a + 1;
        for (; b < n; b++) {
            if ((ar[a] === ar[b]) && ar[b] !== -1) {
                res++;
                ar[a] = -1;
                ar[b] = -1;
            }
        }
    }
    console.log(res)
    return res;
}