#include <stdio.h>
int main()
{
	long long n;
	scanf("%lld", &n);
	if (n >= 1&&n <= 100000000) 
	{
		printf("%lld", ((n+1)*n)/2);
	}
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
    long long n;
    cin>>n;
    cout<<(n+1)*n/2;
    return 0;
}

scanf_s("%d",&x);
for (result = 0, y = 1; y <= x; y++)
{
	result = result + y;


};

printf("%d",result);
return 0;

#include <stdio.h>
int main()
{
    long i,n,sum;
    i = 1;
    sum = 0;
    scanf("%ld",&n);
    do{
        sum = sum+i;
        i++;
    }while(i<=n);
    printf("%ld",sum);
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    long long n = 0;
    long long sum = 0;
    cin >> n;
    for(int i = 1; i <= n; i++)
        sum += i;
    cout << sum << endl;
    return 0;
}

while True:
    try:
        n = input()
        sum = 0
        for i in range(n+1):
            sum += i
        print(sum)
    except:
        break

#include<bits/stdc++.h>
using namespace std;
int main() {
long long  x,y;
scanf("%lld",&x);
printf("%lld\n",((1+x)*x)/2);
    return 0;
}