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#include <iostream>
#include <cmath>
#include <string>
using namespace std;

int main() {

    string str;
    int count = 0;

    cin >> str;

    for (int i = 0; i < str.length(); i++) {
        if (str[i] == 'a') {
            count++;
        }
    }
    cout << count;

    return 0;
}