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]; int mid = (l+r)/2; return sum(x, y, id * 2, l, mid) + sum(x, y, id * 2 + 1, mid, r); }