import sys

def solve():
    n = int(sys.stdin.readline())
    s = list(sys.stdin.readline().strip())
    count = 0
    i = 0
    # n-1 まで
    while i < n - 1:
        # "010" をチェック
        if i + 2 < n and s[i] == '0' and s[i+1] == '1' and s[i+2] == '0':
            s[i+2] = '1' 
            count += 1
        # "00" をチェック 
        elif i + 1 < n and s[i] == '0' and s[i+1] == '0':
            s[i+1] = '1'
            count += 1

        # 次の開始位置へ
        i += 1

    print(count)

if __name__ == "__main__":
    solve()