#include <iostream>
#include <cstdlib>
#include <sstream> 
#include <string> 

int get_sum(int num)
{
    return (num * (num + 1)) >> 1;
}

int main()
{
    std::string line;
    int num = 0;
    for (;getline(std::cin,line);) {
        std::stringstream ss(line);
        ss >> num;
        std::cout << get_sum(num) << std::endl;
    }
    return 0;    
}