def min_operations_to_good_string(n, s):
    ops = 0
    i = 0
    while i < n - 1:
        if s[i] == '0' and s[i + 1] == '0':
            ops += 1
            i += 2
        else:
            i += 1
    return ops

n = int(input())
s = input().strip()

print(min_operations_to_good_string(n, s))