// no.480 合計

#include <iostream>
#include <string>

int main(int argc, char *argv[]);

int main(int argc, char *argv[])
{
    int N;
    
    std::cin >> N;
    std::cout << static_cast<int>(N*(N+1)/2) << std::endl << std::flush;
    
    return 0;
}