import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.StringTokenizer; public class Main { public static void main(String[] args) { FastReader fr = new FastReader(); int n = fr.nextInt(); System.out.println(n*(n+1)/2); } } class FastReader { private final BufferedReader reader = new BufferedReader(new InputStreamReader(System.in), 0x10000); private StringTokenizer tokenizer; String next() { try{ while(tokenizer==null || !tokenizer.hasMoreTokens()) { tokenizer = new StringTokenizer(reader.readLine()); } }catch(IOException e){ e.printStackTrace(); } return tokenizer.nextToken(); } int nextInt() { return Integer.parseInt(next()); } long nextLong() { return Long.parseLong(next()); } double nextDouble(){ return Double.parseDouble(next()); } char[] nextCharArray() { return next().toCharArray(); } char nextSingleChar() { //一文字じゃなかったら' '(空白文字)返す char[] c = next().toCharArray(); if(c.length==1) { return c[0]; }else { return ' '; } } String[] nextStringArray(int n) { String[] s = new String[n]; for (int i = 0; i < n; i++) { s[i] = next(); } return s; } }