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;
	    }

}