Problem:
Score : 100 points

Problem 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?

Constraints

1≦N≦100

Input

The input is given from Standard Input in the following format:

N

Output

Print the necessary number of candies in total.

Sample Input 1

3

Sample Output 1

6

The answer is 1+2+3=6.

Sample Input 2

10

Sample Output 2

55

The sum of the integers from 1 to 10 is 55.

Sample Input 3

1

Sample Output 3

1

Only one child. The answer is 1 in this case.

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
using namespace std;

int main()
{
    string s;
    vector<char> A;
    while(cin>>s)
    {
        int a=s.size();
        for(int i=0;i<a;i++)
        {
            if(s[i]=='0')
            {
            A.push_back('0');
            }
            else if(s[i]=='1')
                    {
                    A.push_back('1');
                    }
                    else if(!A.empty())
                        {
                        A.pop_back();
                        }
        }
        int b=A.size();
        for(int i=0;i<b;i++)
        {
            cout<<A[i];
        }
A.clear();
        cout<<endl;
    }
    return 0;
}