import std.stdio, std.conv, std.functional, std.string; import std.algorithm, std.array, std.container, std.range, std.typecons; import std.numeric, std.math, std.random; import core.bitop; string FMT_F = "%.10f"; static string[] s_rd; T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; } string RDR()() { return readln.chomp; } T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; } size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;} size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; } bool inside(T)(T x, T b, T e) { return x >= b && x < e; } long lcm(long x, long y) { return x * y / gcd(x, y); } long mod = 10^^9 + 7; //long mod = 998244353; void moda(ref long x, long y) { x = (x + y) % mod; } void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; } void modm(ref long x, long y) { x = (x * y) % mod; } void main() { auto N = RD; long ans = N == 1 ? 0 : N; debug writeln(ans); long l = 1, r = N; while (r - l > 1) { auto nl = l + 1; auto nr = r - 1; ans += l * nr; ans += r * nl; debug writeln(nr, ":", l, " ", l * nr); debug writeln(r, ":", nl, " ", r * nl); l = nl; r = nr; } if (l != r) { ans += l * r; debug writeln(l, ":", r, " ", l * r); } writeln(ans); stdout.flush(); debug readln(); }