백준 2355 Java 자바

 

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
 
public class Q2355 {
 
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        long a = Integer.parseInt(st.nextToken());
        long b = Integer.parseInt(st.nextToken());
        
        if(b > a) {
            long temp = b;
            b = a;
            a = temp;
        }
        
        long result = (a+b) * (a-b + 1) / 2;
        System.out.println(result);
 
    }
 
}