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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int main(int argc, char **argv)
{
	string s;
  cin>>s;
  stack <char> stacky;
  for(ll i=0;i<s.size();i++){
    if (s[i]=='1'||s[i]=='0') stacky.push(s[i]);
    else if (s[i]=='B'){
      if (!stacky.empty()) stacky.pop();
    }
    }
  string ans="";
  while (!(stacky.empty())){
    ans+=stacky.top();
    stacky.pop();
  }
  reverse(ans.begin(),ans.end());
  cout<<ans<<"\n";
  
	return 0;
}