N = int(input())
S = list(map(int, list(input())))
count_1 = S.count(1)

for i in range(N):
    if S[i] == 0:
        if i+1 < N:
            S[i+1] = 1
        if i+2 < N:
            S[i+2] = 1
print(S.count(1) - count_1)