a = input()
n = len(a)
i = 0
res = 0
while i<n-1:
if a[i] == a[i+1]:
i += 2
res += 1
elif a[i] != a[i+1]:
if a[i]=='?'or a[i+1] == '?':
i += 2
res += 1
else:
i += 1
print(res)