#include <iostream>
using namespace std;
int main() {
// your code goes here
long long n;cin>>n;
cout<<(n*(n+1))/2;
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwogCmludCBtYWluKCkgewoJLy8geW91ciBjb2RlIGdvZXMgaGVyZQogICAgbG9uZyBsb25nIG47Y2luPj5uOwogICBjb3V0PDwobioobisxKSkvMjsKCXJldHVybiAwOwp9