OK = false ;
while(!OK) {
    in();
    int t = k;
    while(a[t] == n + t - k) t--;
    if(t>0) {
        a[t]++;
        for(int i = t+1; i<= k ; i++) {
            a[i] = a[i-1] +1;
        }
    } else OK = true;
}