int q[N],tmp[N];
int merge_sort(int q[],int l,int r){
    if(l>=r) return ;
    int mid=(l+r)>>1;
    merge_sort(q,l,mid);
    merge_sort(q,mid+1,r);
    int k=0,i=l,j=mid+1;
    while(i<=mid&&j<=r){
        if(q[i]<=q[j]) tmp[k++]=q[i++];
        else tmp[k++]=q[j++];
    }
    while(i<=mid) tmp[k++]=q[i++];
    while(j<=r) tmp[k++]=q[j++];
    for(int i=l,j=0;i<=r;i++,j++) q[i]=tmp[j];
}