s=input()
n=len(s)
ans=0
if s.count('?')==n:
print(n//2)
else:
i=1
while(i<n):
if s[i]==s[i-1]:
ans+=1
i+=2
elif s[i]=='?' or s[i-1]== '?':
ans+=1
i+=2
else:
i+=1
print(ans)