//Normal #define _GLIBCXX_DEBUG #define ll long long #include using namespace std; using Graph = vector>; void print(auto a){ cout << a; } void prints(auto a){ cout << a << " "; } void prints(){ cout << " "; } void printl(auto a){ cout << a << endl; } void printl(){ cout << endl; } void fix(int n){ cout << fixed << setprecision(n); } int siz(string s){ return (int)s.size(); } int ans = 0; vector> dp(110, vector(110, 1e9*-1)); vector> seen(110, vector(110, false)); vector my = {0, 1}; vector mx = {1, 0}; void dfs(vector> &X, int y, int x){ seen[y][x] = true; ans = max(ans, dp[y][x]); for(int i = 0; i < 2; i++){ int MY = y + my[i]; int MX = x + mx[i]; if(seen[MY][MX] or X[MY][MX] == '#') continue; dp[MY][MX] = max(dp[MY][MX], dp[y][x]+1); dfs(X, MY, MX); } } int main(){ int N; cin >> N; printl(N*(N+1)/2); return 0; }