int sum(int x,int y,int id = 1,int l = 0,int r = n){
	if(x >= r or l >= y)	return 0;
	if(x <= l && r <= y)	return s[id];
	shift(id, l, r);
	int mid = (l+r)/2;
	return sum(x, y, id * 2, l, mid) +
	       sum(x, y, id * 2 + 1, mid, r);
}