SumNmber(1-N)

#define _CRT_SECURE_NO_WAR
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define ull unsigned long long int
#define file freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define KingOfWrongAnswer cin.tie(0);std::ios::sync_with_stdio(false);
#define forit(i, a) for ( __typeof( (a).begin() ) i = (a).begin(); i != (a).end(); i++ )
#define mp make_pair
#define pb push_back
#define clr(a,n) memset(a,n,sizeof(a))
#define all(c) c.begin(), c.end()
#define rep(i,n) for(int i=0;i<n;i++)
#define popone(a) __builtin_popcount(a)
#define popzero(a) __builtin_ctz(a)
#define PI = 2.0*acos(0.0)
#define mod 1000000007
#define pi 3.14159265359
//ll gcd (ll x,ll y){if(y==0)return x;return gcd(y,x%y);}
//ll lcm(ll a,ll b){return a/gcd(a,b) * b;}
//int getbit(int n,int i){return ((n>>i)&1)==1;}
//int setbit(int n,int i,int val){return val?(n|(1<<i)):(n&~(1<<i));}
//int graycode(int i){return i^(i>>1);}
//bool power2(int x){return (x && !(x & (x - 1)));}
//ll largest_power(ll n){n = n| (n>>1);n= n| (n>>2);n = n| (n>>4);n = n| (n>>8);return (n+1)>>1;}
//bool cmp(pair<int,int>x,pair<int,int>y){if (x.first==y.first) return x.second>y.second;return x.first<y.first;}
//bool vaild(int x,int y,int n){return (0 <= x && x < n && 0 <= y && y < n);}
//int dx[] = {-1, -1, 1, 1, -2, -2, 2, 2 };
//int dy[] = {2, -2, 2, -2, 1, -1, 1, -1 };
//int dx[] = {0, 0, -1, 1, -1, -1, 1, 1};
//int dy[] = {-1, 1, 0, 0, 1, -1, -1, 1};
//int dx[]= {-1, 1, 0, 0};
//int dy[]= {0, 0, 1, -1};
int main()
{
    KingOfWrongAnswer
    // sum number from 1 to n
    int n;
    cin>>n;
    cout<<(n*(n+1)/2)<<endl;
    return 0;
}