import sys

def solve():
    n = int(sys.stdin.readline())
    s = list(sys.stdin.readline().strip())
    
    count = 0
    i = 0
    while i < n - 1:
        # "00"
        if i + 1 < n and s[i] == '0' and s[i+1] == '0':
            s[i+1] = '1'
            count += 1
            # i+2 から
            i += 2 
        # "010"
        elif i + 2 < n and s[i] == '0' and s[i+1] == '1' and s[i+2] == '0':
            s[i+2] = '1'
            count += 1
            # i+3 から
            i += 3
        else:
            # マッチせず
            i += 1
            
    print(count)

if __name__ == "__main__":
    solve()