N = int(input())
S = input()
ans = 0
i = 0
while i < N:
    if S[i] == '0':
        j = i
        while j < N and S[j] == '0':
            j += 1
        length = j - i
        if length >= 2:
            ans += length - 1
        i = j
    else:
        i += 1
print(ans)