class Solution(object):
    def countBinarySubstrings(self, s):
        ans, prev, cur = 0, 0, 1
        for i in xrange(1, len(s)):
            if s[i-1] != s[i]:
                ans += min(prev, cur)
                prev, cur = cur, 1
            else:
                cur += 1
        return ans + min(prev, cur)