#include <iostream>
using namespace std;
int main() {
int x,y=0;
cin>>x;
while(x>0){
y=y+x;
x--;
}
cout<<y;
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgogICAKdXNpbmcgbmFtZXNwYWNlIHN0ZDsKICAgCmludCBtYWluKCkgewogICAgaW50IHgseT0wOwogICAgY2luPj54OwogIHdoaWxlKHg+MCl7CiAgICAgIHk9eSt4OwogICAgICAgICAgeC0tOwogIH0KICAgIGNvdXQ8PHk7CiAgICByZXR1cm4gMDsKfQ==