using System;
public class Program
{
public static void Main()
int n;
do{
Console.Write("กรุณาใส่ตัวเลข 1-100 : ");
n= int.Parse(Console.ReadLine());
}while(n<1 || n>100);
int sum=0, i;
for(i=1;i<=n; i++){
sum += i;
}
Console.WriteLine("Sum of 1-{0} : {1} ",n,sum);
//Console.WriteLine("");