#include <bits/stdc++.h>
#define ll long long
#define YES cout << "YES\n";
#define NO cout << "NO\n";
#define opps cout<<-1<<endl;
const ll con = 1e10 + 5;
using namespace std;
class rectangle {
    double height ;
    double width ;
    public:
    rectangle();
    double get_area() ;
    double get_perimeter() ;
    double get_height() ;
    double get_width() ;
    void set_width(double width_) ;
    void set_height(double height_) ;
};
rectangle::rectangle() {
    width = height = 0;
}
double rectangle::get_area() {
    return width * height;
}
double rectangle::get_perimeter() {
    return width + height ;
}
double rectangle::get_height() {
    return height;
}
double rectangle::get_width() {
    return width;
}
void rectangle::set_height(double height_) {
    height = height_;
}
void rectangle::set_width(double width_) {
    width = width_;
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    ll n ;
    cin>>n;
    ll sum = ((n * (n+1)) / 2);
    cout<<sum;
}