[백준][Python] 1439번 뒤집기

S = input()
count0 = 0
count1 = 0
if S[0] == "1" :
    count0 += 1
else :
    count1 += 1
for i in range(len(S)-1):
    
    if S[i] != S[i + 1]:
        
        if S[i + 1] == "0":
            count1 += 1
        else :
            count0 += 1
print(min(count0,count1))