nikita.cpp

#include <bits/stdc++.h>

#define rep(x, s, e) for (int x = int(s); x < int(e); ++x)

using namespace std;

int main() {
  string s;
  cin >> s;

  // Create prefix arrays counting a's and b's *before* position
  vector<int> a(s.size() + 1);
  vector<int> b(s.size() + 1);
  a[0] = b[0] = 0;
  rep(i, 0, s.size()) {
    a[i + 1] = a[i] + (s[i] == 'a'); // true is converted to 1, false to 0
    b[i + 1] = b[i] + (s[i] == 'b');
  }

  int ret = 0;
  rep(i, 0, s.size() + 1) {    // Letter after first part
    rep(j, i, s.size() + 1) {  // Letter after middle part
      int first = a[i];
      int middle = b[j] - b[i];
      int last = a.back() - a[j];
      ret = max(ret, first + middle + last);
    }
  }
  cout << ret << endl;

  return 0;
}