static int[] merge(int[] a,int[] b){
        if (a.length==0)
            return b;
        if (b.length==0)
            return a;
        if (a[0]<b[0]){
            int t = a[0];
            int[] r = new int[a.length-1];
            for(int i = 0 ; i < r.length ; i++){
                r[i]= a[i+1];
            }
            return mergeConcat(t,merge(r,b));
           
        }
        else{
            int t = b[0];
            int[] r = new int[b.length-1];
            for(int i = 0 ; i < r.length ; i++){
                r[i]= b[i+1];
            }
            return mergeConcat(t,merge(a,r));
        }
    }