def calc(st: list) -> int: res = 0 l = 0 for h, v in reversed(st): res += (h - l) * v l = h return res INF = 1 << 60 N = int(input()) H = list(map(int, input().split())) st = [(INF, 0, 0)] for i, h in enumerate(H): v = 1 if i % 2 == 0 else 0 # 1=水色 while st[-1][0] <= h: st.pop() w = st[-1][2] if st[-1][1] == 0: w += h * v elif st[-1][1] == 1: if v == 0: w -= h print(w) st.append((h, v, w))