"""
[1439: 뒤집기](https://www.acmicpc.net/problem/1439)
Tier: Silver 5
Category: 구현
"""
def solution():
s = input()
cnt = 1
for i in range(1, len(s)):
if s[i - 1] != s[i]:
cnt += 1
return cnt // 2
if __name__ == '__main__':
print(solution())