public class Solution {
/* public int Sum_Solution(int n) {
if(n < 1){
return 0;
}
return n + Sum_Solution(n - 1);
}
*/
public int Sum_Solution(int n){
if(n < 1){
return 0;
}
int temp = (int)Math.pow(n , 2) + n;
return temp >> 1;
}
}