void main(){
  import std.stdio, std.string, std.conv, std.algorithm;
  import std.range;

  string s; rd(s);

  int m=0;
  foreach(i, c; s){
    if(c=='A') continue;
    foreach(j; i..s.length)if(s[j]=='A') m++;
  }

  writeln(m);
}

void rd(T...)(ref T x){
  import std.stdio, std.string, std.conv;
  auto l=readln.split;
  foreach(i, ref e; x){
    e=l[i].to!(typeof(e));
  }
}