// SumFromOneToN.java

class SumFromOneToN {
	
	public static void main(String[] args) {
		// describe the program
		System.out.println("This program demonstrates using a 'for' loop");
		System.out.println("to count from 1 to n.");
		
		// declare three integer variables
		int n, sum, counter;
		
		// loop forever
		while (true) {
			// read in a value for n
			System.out.println();
			System.out.print("Enter an integer value [or <=0 to exit]: ");
			n = readInt();
			
			// if the user entered a non-positive number, exit the program
			if (n <= 0) {
				System.exit(0);
			}
			
			// start with the sum set to 0
			sum = 0;
			
			// use a "for" loop to count from 1 to n
			for (counter=1; counter<=n; counter++) {
				sum = sum + counter;
			}
			
			// report the sum
			System.out.print("The sum from 1 to ");
			System.out.print(n);
			System.out.print(" = ");
			System.out.println(sum);
		}
	}
	
	///////////////////////////////////
	// readString, readInt, readDouble
	///////////////////////////////////
	
	public static String readString() {
		java.io.InputStreamReader isr = new java.io.InputStreamReader(System.in);
		java.io.BufferedReader d = new java.io.BufferedReader(isr);
		try { return d.readLine(); } catch (Exception e) { return "error"; }
	}
	public static int readInt() { return Integer.parseInt(readString()); }
	public static double readDouble() {
		return Double.valueOf(readString()).doubleValue();
	}
}