[백준] 3046번 : R2 - Dart(다트)

https://www.acmicpc.net/problem/3046

import 'dart:io';
void main(){
    String? sc=stdin.readLineSync();
    final v=sc!.split(' ').map<int>((o)=>int.parse(o));
    var r=v.elementAt(0);
    var s=v.elementAt(1);
    print(2*s-r);
}