import sys
input = sys.stdin.readline
N = int(input())
S = input().strip()
ans = 0
cnt = N
for i in range(N):
    s = S[i]
    if s=="0":
        if cnt<2:
            ans += 1
            cnt += 1
        else:
            cnt = 0
    else:
        cnt += 1
print(ans)