import java.util.function.Function;

public class Sum {

    /** Returns the accumulated sum from i = a to b of f(i). */
    public static double sum(Function<Integer, Double> f, int a, int b) {
        double result = 0.0;

        for (int i = a; i <= b; i++) {
            result += f.apply(i);
        }

        return result;
    }

    public static void main(String[] args) {
        int a = Integer.parseInt(args[0]);
        int b = Integer.parseInt(args[1]);

        System.out.print("Sum from " + a + " to " + b + ": ");
        System.out.println(sum((x) -> (double) x, a, b));
    }
}