output_description: Print the necessary number of candies in total.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N
attempt: #include <algorithm>
  #include <iostream> //入出力
  #include <stdio.h>
  #include <map>
  #include <set>
  #include <string>
  #include <math.h> //算術演算子
  #include <vector>
  #include <cstdlib>
  #include <queue>
  #include <stack>
  #include <list>
  #include <iomanip> //小数点以下を表示させる(setprecision())
  // #include <bits/stdc++.h>
  using namespace std;
  typedef long long ll; //64bit型
  
  #define rep(i, n) for (int i = 0; i < (n); i++)
  #define all(a) (a).begin(), (a).end()
  #define debug(x) cerr << x << " " \
                        << "(L:" << __LINE__ << ")" << '\n'
  #define PRINT(V)                                   \
          {                                          \
                  for (int i = 0; i < V.size(); i++) \
                  {                                  \
                          cout << V[i] << " ";       \
                  }                                  \
                  cout << endl;                      \
          }
  
  int gcd(int a, int b)
  {
          return b ? gcd(b, a % b) : a;
  }
  
  int main() //input->compute->output
  {
          int N, K;
          cin >> N;
  
          cout << N * (N +1) / 2 << endl;
  
          return 0;
  }
problem_description: Statement
  
  There are N children in AtCoder Kindergarten. Mr. Evi will arrange the
  children in a line, then give 1 candy to the first child in the line, 2
  candies to the second child, ..., N candies to the N-th child. How many
  candies will be necessary in total?
samples: [{"input": "3", "output": "6\n    \n\nThe answer is 1+2+3=6.\n\n* * *"}, {"input": "10", "output": "55\n    \n\nThe sum of the integers from 1 to 10 is 55.\n\n* * *"}, {"input": "1", "output": "1\n    \n\nOnly one child. The answer is 1 in this case."}]