//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int siz(string s){
  return (int)s.size();
}

int ans = 0;
vector<vector<int>> dp(110, vector<int>(110, 1e9*-1));

vector<vector<bool>> seen(110, vector<bool>(110, false));
vector<int> my = {0, 1};
vector<int> mx = {1, 0};

void dfs(vector<vector<char>> &X, int y, int x){
  seen[y][x] = true;
  ans = max(ans, dp[y][x]);
  
  for(int i = 0; i < 2; i++){
    int MY = y + my[i];
    int MX = x + mx[i];
    
    if(seen[MY][MX] or X[MY][MX] == '#') continue;
    dp[MY][MX] = max(dp[MY][MX], dp[y][x]+1);
    dfs(X, MY, MX);
  }
}

int main(){
  int N; cin >> N;
  
  printl(N*(N+1)/2);
  return 0;
}