SP2129 CAKE2 - Cake

Some time ago a VERY huge cake was made in the village called Nalomena Trieska. Well, it was infinitely large and infinitely thin. For our needs it looked exactly like an infinite plane. It was not very tasty, so nobody wanted to eat it. Instead, local children started to play with it. Each of them drew one straight line on the plane. These lines divided the plane into many parts. For a few hours the children were happy, they jumped from one part into another and played other similar games. But then little Tommy suddenly asked: "How many parts does the cake have?" "1999." answered Martin. "No, 2000 !" replied Richard. "Well, I think it's only 1748." stated Michael. And they started to argue. Now their parents need your help, because the children spend all their time counting the parts of the cake.

The first line of the input file contains the number of straight lines N(N

The output file contains a single integer giving the number of parts into which given N lines divide the plane.