/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static long getBaseTen(String binary)
    {
        long ten=0;
        for (int i = 0; i < binary.length(); i++)
        {
            if (binary.charAt(i) == '1')
                ten += Math.pow(2,  binary.length()-i-1);
        }
        return ten;
    }
 
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(getBaseTen("10101"));
	}
}

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