function Main(input) {
    const S = input[0];
    
    var currentA = 0;
    var sum = 0;
    var prevB = false;
    console.log(S);
    
    for (var index = 0; index < S.length; index++) {
        var element = S.charAt(index);
        if(element === "A") {
            currentA++;
        }else if(element === "B") {
            if(prevB) { 
                currentA = 0;
            }
        } else {
            if(prevB) {
                sum += currentA;
            } else {
                currentA = 0;
            }
        }
        prevB = element === "B";
    }

    console.log(sum);
    
}

// 1行入力の場合
// Main(require("fs").readFileSync("/dev/stdin", "utf8").trim());

// 改行で分割
// Main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split(/\n/));

// 改行・空白で分割
Main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split(/\n|\s/));