建議自己寫一遍這題很簡單

import java.util.Scanner;

public class b294 {
    public static void main (String[]args){
        Scanner input = new Scanner(System.in);
        if (input.hasNextInt()){
            int n = input.nextInt();
            int answer = 0;
            for (int i=1;i<n+1;i++){
                answer += input.nextInt()*i;
            }
            System.out.println(answer);
        }
    }
}