import copy

C = 0
fla = 0

def migi(M):
    M.pop(0)
    return(M)

def sita(M):
    L = []
    for i in M:
        if i - 1 > 0:
            L.append(i-1)

    return(L)

def migisita(M):
    org = copy.deepcopy(M)
    global C
    global fla
    
    if len(M):
        fla = 1
        M = migi(M)
        if len(M):
            migisita(M)
    if len(M) ==0:

        if fla == 1:
            C += 1
            fla = 0
    M = copy.deepcopy(org)
    if len(M):
        fla = 1
        M = sita(M)

        if len(M):
            migisita(M)

    if len(M) ==0:
        if fla == 1:
            C += 1
            fla = 0


N = int(input())
M = list(map(int, input().split()))

migisita(M)
print(C)