#include <iostream>
using namespace std;

int main() {
    int N;
    cin >> N; // 输入第一步走的厘米数

    // 计算等差数列的和
    long long total_distance = (long long)N * (N + 1) / 2;

    // 输出总共走的厘米数
    cout << total_distance << endl;

    return 0;
}
/**************************************************************
	Problem: 2100
	User: admin
	Language: C++
	Result: Accepted
	Time:53 ms
	Memory:2072 kb
****************************************************************/