#include <iostream>
using namespace std;
int main() {
double n;
cin>>n;
long long sum = 0;
sum = (1+n)*n/2;
cout<<sum;
return 0;
}
#include <iostream>
using namespace std;
int main() {
double n;
cin>>n;
long long sum = 0;
sum = (1+n)*n/2;
cout<<sum;
return 0;
}