※주의
package BeakJoon;
import java.io.*;
public class B8393 {
public static void main(String[] args) throws IOException {
BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
int n = Integer.parseInt(bf.readLine());
int result = 0;
if(n >= 1 && n <= 10000) {
for (int i = 0; i <= n; i++) {
result += i;
}
}
bw.write(String.valueOf(result));
bw.close();
}
}