Monkey eating peach problem (loop, recursion)

7-17 h0158. The problem of monkeys eating peaches (10 branch )

There is a pile of peaches , The monkey ate half of it on the first day , And one more ！ Later, every day monkeys eat half of them , And then one more . When it comes to the third n days , When you want to eat again （ Haven't eaten yet ）, Only found 1 A peach . problem ： How many peaches are there in the first place ？

Input format :

Give... In one line 1 No more than one. 30 The positive integer n.

Output format :

Output the initial number of peaches in one line .

sample input :

10

sample output :

 Peach =1534

import scala.io.StdIn;
object Main{
    def main(args: Array[String]) : Unit = {
        var n = StdIn.readInt();
        var sum = 1;
        for ( i <- 1 to n - 1) {
            sum = (sum + 1) * 2;
        }
        println(" Peach ="+sum);
    }
}

import scala.io.StdIn
object Main {
    def main(args: Array[String]): Unit = {
        var n = StdIn.readInt();
        val num = f(1,1,n);
        print(" Peach ="+num);
    }
    def f(a : Int ,d : Int ,n : Int): Int = {
        var ans = (a + 1) * 2;
        var dcnt = d + 1;
        if(dcnt == n) return ans;
        else f(ans ,dcnt ,n);
    }
}