using System;
using System.IO;
using System.Collections.Generic;
using static System.Console;
using static System.Math;
class Start{
  static void Solve(){
  	var n=Rint();
  	Write(n*(n+1)/2+LF);
  }
  static void Main(){
  	string s,t="";
  	readcount=-1;
  	while(true){
  		s=ReadLine();
  		if(s==null)break;
  		t+=s.Trim()+" ";
  	}
  	read=t.Split();
    var sw=new StreamWriter(OpenStandardOutput()){AutoFlush=false};
    SetOut(sw);
    Solve();
    Out.Flush();
  }
  static string Read(){readcount++;return read[readcount];}
  static int Rint(){readcount++;return int.Parse(read[readcount]);}
  static long Rlon(){readcount++;return long.Parse(read[readcount]);}
  static double Rdou(){readcount++;return double.Parse(read[readcount]);}
  static char Rcha(){readcount++;return read[readcount][0];}
  static string[] read;static int readcount;
  const long MOD=1000000007L;
  const string LF="\n";
  static void Swap<T>(ref T a,ref T b){T c=a;a=b;b=c;}
}
class Pair<T1,T2>:IComparable<Pair<T1,T2>>where T1:IComparable<T1>where T2:IComparable<T2>{
  public T1 F;public T2 S;
  public Pair(T1 f,T2 s){F=f;S=s;}
  public int CompareTo(Pair<T1,T2> p)=>F.CompareTo(p.F)!=0?F.CompareTo(p.F):S.CompareTo(p.S);
  public override string ToString()=>F+" "+S;
}