import sys
input = sys.stdin.readline

def main():
    N = int(input())
    S = input().rstrip()
    total0 = S.count('0')

    # dp[0]=0, dp[1], dp[2] まで扱えるように長さ N+1 の配列を確保
    dp = [0] * (N+1)

    for i in range(1, N+1):
        if S[i-1] == '1':
            dp[i] = dp[i-1]
        else:  # S[i-1] == '0'
            keep = 1
            if i >= 3:
                keep += dp[i-3]
            dp[i] = max(dp[i-1], keep)

    ans = total0 - dp[N]
    print(ans)

if __name__ == '__main__':
    main()