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(ref T a,ref T b){T c=a;a=b;b=c;} } class Pair:IComparable>where T1:IComparablewhere T2:IComparable{ public T1 F;public T2 S; public Pair(T1 f,T2 s){F=f;S=s;} public int CompareTo(Pair p)=>F.CompareTo(p.F)!=0?F.CompareTo(p.F):S.CompareTo(p.S); public override string ToString()=>F+" "+S; }