Seeking Sn = a + aa + aaa + ... + aa ... aaa (with n a) of the value, where a is a number of 2. For example, n = 5 when = 2 + 22 + 222 + 2222 + 22222, n input from the keyboard.

1013 problem: [introductory programming] Sn the sum formula

Time limit: 1Sec Memory Limit: 128MB submission: 8018 Resolution: 5541

Title Description

Seeking Sn = a + aa + aaa + ... + aa ... aaa (with n a) of the value, where a is a number of 2. For example, n = 5 when = 2 + 22 + 222 + 2222 + 22222, n input from the keyboard.

Entry

n

Export

The value of Sn

Sample input

5

Sample Output

24690 

Analysis: 
When For n = 3, i is 1 ~ n

　i=1  2*10^i-1=2
    i=2  2*10^i-1+2*10^i-2=22
    i=3  2*10^i-1+2*10^i-2+2*10^i-3=222

　......

import java.util.Scanner;
import java.math.*;
public class Main {
public static void main(String[] args) {
　　Scanner in = new Scanner(System.in);
　　int sum=0;
　　int n = in.nextInt();
　　for(int i =1;i<=n;i++){
　　　　sum+=fun(i);
　　}
　　System.out.println(sum);
}
public static int fun(int m){
　　int num=0;
　　for(int i=0;i<m;i++){
　　　　num+=2*Math.pow(10, i);
}
　　return num;
}

}