#include <iostream>
using namespace std;
int main()
{ string s;
  int j=0,k=0;
  bool b;
  getline(cin,s);
  do
  { k=s.find("a",k+1);
    b=((0<=k)&&(k<s.size()));
    if (b) j++;
  }
  while(b);
  cout<<j;
  return 0;
}