N = int(input())
S = input()

INF = 1<<60

dp = [[INF]*3 for _ in range(N+1)]
dp[0][0] = 0
for i in range(N):
    for j in range(3):
        if dp[i][j] == INF:
            continue
        if S[i] == "1":
            dp[i+1][max(j-1, 0)] = min(dp[i+1][max(j-1, 0)], dp[i][j])
        else:
            if j == 0:
                dp[i+1][2] = min(dp[i+1][2], dp[i][j])
            dp[i+1][max(j-1, 0)] = min(dp[i+1][max(j-1, 0)], dp[i][j]+1)

print(min(dp[-1]))