n = int(input())
S = list(input())
tot = 0
mi = False
ma = 0
ind = -1
for i, s in enumerate(S):
    if s == "+":
        tot += 1
    elif s == "-":
        tot -= 1
    else:
        tot += 1
    if tot < 0:
        if not mi:
            mi = True
            ind = i
    if mi:
        ma = max(ma, tot)

if not mi:
    print(0)
    exit()

for i in range(ind - 1, -1, -1):
    if S[i] == "?":
        if ma > 0:
            S[i] = "-"
            ma -= 1
        else:
            S[i] = "+"

if ma > 0:
    print(2)
    exit()
tot = 0
for i in range(ind):
    if S[i] == "+":
        tot += 1
    else:
        tot -= 1
    if tot < 0:
        print(2)
        exit()
print(1)