import java.io.OutputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.StringTokenizer; import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.InputStream; /** * Built using CHelper plug-in * Actual solution is at the top * * @author Chiaki.Hoshinomori */ public class Main { public static void main(String[] args) { InputStream inputStream = System.in; OutputStream outputStream = System.out; InputReader in = new InputReader(inputStream); PrintWriter out = new PrintWriter(outputStream); Task480 solver = new Task480(); solver.solve(1, in, out); out.close(); } static class Task480 { public void solve(int testNumber, InputReader in, PrintWriter out) { int n = in.nextInt(); out.println(n * (n + 1) / 2); } } static class InputReader { public BufferedReader reader; public StringTokenizer tokenizer; public InputReader(InputStream stream) { reader = new BufferedReader(new InputStreamReader(stream), 32768); tokenizer = null; } public String next() { while (tokenizer == null || !tokenizer.hasMoreTokens()) { try { tokenizer = new StringTokenizer(reader.readLine()); } catch (IOException e) { throw new RuntimeException(e); } } return tokenizer.nextToken(); } public int nextInt() { return Integer.parseInt(next()); } } }