백준 - 26005번

 

풀이

 

import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
    	BufferedReader br   = new BufferedReader(new InputStreamReader(System.in));
        int num             = Integer.parseInt(br.readLine());
        int result          = 0;
        
        if(num >= 2) {
            result = num * num / 2;
            if(num % 2 == 1) result++;
        } 
    	
    	System.out.println(result);
    }
}