def min_operations_to_good_string(n, s):
    operations = 0
    i = 0

    while i < n:
        if s[i] == '0':
            j = i
            while j < n and s[j] == '0':
                j += 1
            length = j - i
            if length >= 2:
                operations += (length + 1) // 2
            i = j
        else:
            i += 1

    return operations

if __name__ == "__main__":
    n = int(input())
    s = input().strip()
    min_operations_to_good_string(n, s)