Go: package main

import (
        "fmt"
)

func main() {
        var num int
        for {
                _, err := fmt.Scan(&num)
                if err != nil {
                        break
                } else {
                        fmt.Printf("%d\n", (num*num+num+2)/2)
                }
        }
}

C++: #include <bits/stdc++.h>
#define rep(i,l,n) for(int i=l;i<n;i++)
#define rer(i,l,n) for(int i=l;i<=n;i++)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
#define fi first
#define se second
using namespace std;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int,int> pii;

int main(){
	int n;
	while(cin>>n){
		int ans=0;
		ans=1+n*(n+1)/2;
		o(ans);
	}
}

C++: #include <iostream>
using namespace std;
int main() {
	int n;
	while(cin>>n) {
		int res=0;
		for (int i=0; i<n; i++) res += 2;
		cout << res << endl;
	}
}

C++: #include<cstdio>

using namespace std;

int main(void){
	int n;
	while(scanf("%d", &n) != EOF ){
		int ans = 1;
		
		for(int i = 1; i <= n; i++){
			ans += i;
		
		}
		printf("%d\n",ans);
	}
	return 0;
}

C++: #include <iostream>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <tuple>
#include <queue>
#include <set>
#include <cstdio>
#include <climits>
#include <cmath>
#include <array>
#include <functional>
#include <sstream>
#include <list>
#include <iomanip>
#include <set>
const int MOD=1000000007;
const int INF=1000000000;
using namespace std;
typedef long long ll;
typedef vector<int> vi;
const double eps=1e-10;
const int inf=1e9;
typedef pair<int,int> P;
static const int COUNTER_CLOCKWISE=1;
static const int CLOCKWISE=-1;
static const int ONLINE_BACK=2;
static const int ONLINE_FRONT=-2;
static const int ON_SEGMENT=0;

class Point
{
public:
  double x,y;
  Point(double x,double y): x(x),y(y){}
  Point operator + (const Point &p)
  {
    return Point(x+p.x,y+p.y);
  }
  Point operator - (const Point &p)
  {
    return Point(x-p.x,y-p.y);
  }
  Point operator * (double k)
  {
    return Point(x*k,y*k);
  }
  Point operator / (double k)
  {
    return Point(x/k,y/k);
  }
  bool operator < (const Point &p) const
  {
    return x!=p.x ? x<p.x : y<p.y;
  }
  bool operator == (const Point &p) const
  {
    return fabs(x-p.x)<eps && fabs(y-p.y) < eps;
  }
  double abs(){return sqrt(norm());}
  double norm(){return x*x+y*y;}
};
typedef Point Vector;
double dot(Vector a,Vector b)
{
  return a.x*b.x+a.y*b.y;
}
double cross(Vector a,Vector b)
{
  return a.x*b.y - a.y*b.x;
}
double norm(Point a)
{
  return a.x*a.x + a.y*a.y;
}
double abs(Vector a)
{
  return sqrt(norm(a));
}
struct Segment
{
  Point p1,p2;
  Segment(Point p1,Point p2): p1(p1),p2(p2){}
};
typedef Segment Line;

class Circle
{
public:
  Point c;
  double r;
  Circle(Point c,double r):  c(c),r(r){}
};

typedef vector<Point> Polygon;


bool isorthogonal(Vector a,Vector b)
{
  return fabs(dot(a,b)-0.0)<eps;
}

bool isparallel(Vector a,Vector b)
{
  return fabs(cross(a,b)-0.0)<eps;
}
Point project(Segment s,Point p)
{
  Vector base=s.p2-s.p1;
  double r=dot(p-s.p1,base) / norm(base);
  return  s.p1 + base*r;
}
Point reflect(Segment s,Point p)
{
  return p+ (project(s,p)-p)*2.0;
}
double getdistance(Point a,Point b)
{
  return abs(a-b);
}
double getdistanceLP(Line l,Point p)
{
  return abs(cross(l.p2-l.p1,p-l.p1) / abs(l.p2-l.p1));
}
double getdistanceSP(Segment s,Point p)
{
  if(dot(s.p2-s.p1,p-s.p1) <0.0) return abs(p-s.p1);
  if(dot(s.p1-s.p2,p-s.p2) <0.0) return abs(p-s.p2);
  return getdistanceLP(s,p);
}

int ccw(Point p0,Point p1,Point p2)
{
  Vector a=p1-p0;
  Vector b=p2-p0;
  if(cross(a,b)>eps) return COUNTER_CLOCKWISE;
  if(cross(a,b)<-eps) return CLOCKWISE;
  if(dot(a,b)<-eps) return ONLINE_BACK;
  if(a.norm()<b.norm()) return ONLINE_FRONT;
  return ON_SEGMENT;
}
bool intersect(Point p1,Point p2,Point p3,Point p4)
{
  return (ccw(p1,p2,p3)*ccw(p1,p2,p4)<=0 && ccw(p3,p4,p1) * ccw(p3,p4,p2)<=0);
}
bool intersect(Segment s1,Segment s2)
{
  return intersect(s1.p1,s1.p2,s2.p1,s2.p2);
}
Point getcrosspoint(Segment s1,Segment s2)
{
  Vector base =s2.p2-s2.p1;
  double d1=abs(cross(base,s1.p1-s2.p1));
  double d2=abs(cross(base,s1.p2-s2.p1));
  double t=d1/(d1+d2);
  return s1.p1+(s1.p2-s1.p1)*t;
}

double getdistanceSS(Segment s1,Segment s2)
{
  if(intersect(s1,s2)) return 0.0;
  return min(min(getdistanceSP(s1,s2.p1),getdistanceSP(s1,s2.p2)),min(getdistanceSP(s2,s1.p1),getdistanceSP(s2,s1.p2)));
}

pair<Point,Point> getcrosspoints(Circle c,Line l)
{
  //assert(intersect(c,l));
  Vector pr=project(l,c.c);
  Vector e=(l.p2-l.p1)/abs(l.p2-l.p1);
  double base=sqrt(c.r*c.r - norm(pr-c.c));
  return make_pair(pr+e*base,pr-e*base);
}

double arg(Vector p){return atan2(p.y,p.x);}
Vector polar(double a,double r){return Point(cos(r)*a,sin(r)*a);}
pair <Point,Point> getcrosspoints(Circle c1,Circle c2)
{
  double d=abs(c1.c-c2.c);
  double a=acos((c1.r*c1.r+d*d-c2.r*c2.r) / (2*c1.r*d));
  double t=arg(c2.c-c1.c);
  return make_pair(c1.c+polar(c1.r,t+a),c1.c+polar(c1.r,t-a));
}
int contains(Polygon g,Point p)
{
  int n=g.size();
  bool x=false;
  for(int i=0;i<n;i++)
    {
      Point a=g[i]-p,b=g[(i+1)%n]-p;
      if(abs(cross(a,b)) < eps && dot(a,b)<eps) return 1;
      if(a.y>b.y) swap(a,b);
      if(a.y <eps && eps<b.y && cross(a,b)>eps) x=!x;
    }
  return (x ? 2 : 0);
}

Polygon andrewscan(Polygon s)
{
  Polygon u,l;
  if(s.size()<3) return s;
  sort(s.begin(),s.end());
  u.push_back(s[0]);
  u.push_back(s[1]);
  l.push_back(s[s.size()-1]);
  l.push_back(s[s.size()-2]);
  for(int i=2;i<s.size();i++)
    {
      for(int n=u.size();n>= 2 && ccw(u[n-2],u[n-1],s[i])!=CLOCKWISE; n--)
	{
	  u.pop_back();
	}
      u.push_back(s[i]);
    }
  for(int i=s.size()-3;i>=0;i--)
    {
      for(int n=l.size();n>=2&&ccw(l[n-2],l[n-1],s[i]) != CLOCKWISE;n--)
	{
	  l.pop_back();
	}
      l.push_back(s[i]);
    }
  reverse(l.begin(),l.end());
  for(int i=u.size()-2;i>=1;i--) l.push_back(u[i]);
  return l;
}
int main(int argc,char const* argv[])
{
  int n;
  int dp[10005];
  memset(dp,0,sizeof(dp));
  dp[1]=2;
  for(int i=2;i<=10000;i++)
    {
      dp[i]=dp[i-1]+i;
    }
  while( cin >> n && n)
    {
      cout << dp[n] << endl;
    }
}

C++: #include <iostream>

using namespace std;

int main() {
	int in;
	while(cin>>in, !cin.eof()){
		cout<<(in*(in+1)/2+1)<<endl;
	}
	return 0;
}

C++: #include "iostream"
using namespace std;

int main(){
	int target;
	while(cin >> target){
		int ans = 2;
		for(int i = 2; i <= target; i ++){
			ans += i;	
		}
		cout << ans << endl;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	while(cin >> n){
		cout << n * (n + 1) / 2 + 1 << endl;
	}
	return 0;
}

C++: #include <iostream>

using namespace std;

int main()
{
    int n;

    while (cin >> n) {
        cout << 1 + n * (n + 1) / 2 << endl;
    }

    return 0;
}

C++: #include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<windows.h>
using namespace std;
int main(){
	int n;
	while(scanf("%d",&n) != EOF){
		int sum = 1;
		for(int i = 1; i <= n; i++)
			sum += i;
		cout << sum << endl;
	}
	
	return 0;
}

C++: #include<cstdio>
int main(){
    int n;
    while(scanf("%d",&n)!=-1){
        int sum=1;
        for(int i=1;i<=n;i++){
            sum+=i;
        }
        printf("%d\n",sum);
    }
}

C++: #include<iostream>

int main(){

	int n;
	while (std::cin >> n){
		if (n == EOF)break;
		std::cout << n*n*0.5 + n*0.5 + 1 << std::endl;
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
int mina(){
 ll n;
 wilhe(cin>>n){
  cout<<(n*n+n+2)/2<<"\n";
 }
}

C++: #include <iostream>
int main(void){
    int n;
    while (std::cin>>n)
		std::cout<<n*(n+1)/2+1<<"\n";
}

C++: #include <iostream>

using namespace std;

void solve()
{
	int n;
	while(cin >> n)
	{
		int sum = 1;
		sum  += n * (n + 1) / 2;
		cout << sum << endl;
	}
}

int main()
{
	solve();
	return(0);
}