using System;
class Start
{
    static void Main()
    {
        long n;Inl(out n);
        Outl((n + 1) * n / 2);
    }

    static void Inl(out long t) { t = long.Parse(Console.ReadLine()); }
    static void Inl(out string t) { t = Console.ReadLine(); }
    static void Inl(out char t) { t = Console.ReadLine()[0]; }
    static void Inl(out double t) { t = double.Parse(Console.ReadLine()); }
    static void Inl<T>(ref T[] t)
    {
        string[] s = Console.ReadLine().Split();
        Type type = typeof(T);
        int n = s.Length;
        if (type == LONG) for (int i = 0; i < n; i++) t[i] = (T)(object)long.Parse(s[i]);
        else if (type == STRING) for (int i = 0; i < n; i++) t[i] = (T)(object)s[i];
        else if (type == CHAR) for (int i = 0; i < n; i++) t[i] = (T)(object)s[i][0];
        else for (int i = 0; i < n; i++) t[i] = (T)(object)double.Parse(s[i]);
    }
    static void Inl<T, U>(out T t, out U u) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); }
    static void Inl<T, U, V>(out T t, out U u, out V v) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); In(out v, ref s, 2); }
    static void Inl<T, U, V, W>(out T t, out U u, out V v, out W w) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); In(out v, ref s, 2); In(out w, ref s, 3); }
    static void Inl<T, U, V, W, X>(out T t, out U u, out V v, out W w, out X x) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); In(out v, ref s, 2); In(out w, ref s, 3); In(out x, ref s, 4); }
    static void Inl<T, U, V, W, X, Y>(out T t, out U u, out V v, out W w, out X x, out Y y) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); In(out v, ref s, 2); In(out w, ref s, 3); In(out x, ref s, 4); In(out y, ref s, 5); }
    static void Inl<T, U, V, W, X, Y, Z>(out T t, out U u, out V v, out W w, out X x, out Y y, out Z z) { string[] s = Console.ReadLine().Split(); In(out t, ref s, 0); In(out u, ref s, 1); In(out v, ref s, 2); In(out w, ref s, 3); In(out x, ref s, 4); In(out y, ref s, 5); In(out z, ref s, 6); }
    static void In<T>(out T t, ref string[] s, int i)
    {
        Type type = typeof(T);
        if (type == LONG) t = (T)(object)long.Parse(s[i]);
        else if (type == STRING) t = (T)(object)s[i];
        else if (type == CHAR) t = (T)(object)s[i][0];
        else t = (T)(object)double.Parse(s[i]);
    }
    static Type LONG = typeof(long);
    static Type STRING = typeof(string);
    static Type CHAR = typeof(char);

    static void Out<T>(T t) { Console.Write(t); }
    static void Outl<T>(T t) { Console.WriteLine(t); }

    static void Swap<T>(ref T a, ref T b) { T c = a; a = b; b = c; }
}