f=open('24.txt')
s=f.readline().strip()
k=0
ka=0
for i in range(len(s)-2):
    if s[i]!=s[i+1] and s[i]!=s[i+2] and s[i+1]!=s[i+2]:
        if 'a' in s[i:i+3]:
            ka+=1
        if 'a' not in s[i:i+3]:
            k+=1
print(abs(k-ka))