import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		long n = Long.parseLong(br.readLine());
		br.close();

		BigInteger bn = BigInteger.valueOf(n);

		BigInteger ans = bn.multiply(bn.add(BigInteger.ONE)).divide(BigInteger.valueOf(2));
		System.out.println(ans.toString());
	}
}