function main(input) {
  const R = parseInt(input.split(" ")[0], 10);
  if(R<1200){
    console.log("ABC");
  }else if(R<2800){
    console.log("ARC");
  }else{
    console.log("AGC");
  }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));