StringIndexOutOfBound error !!! plz give me the reason for this error ,plz.........

import java.util.Scanner;

class Even {

static int getEven(int firstno,int secondno)

{
int counteven=0;

for(int i=firstno;i<=secondno;i++)

   {
        if(i%2==0)
        {
            counteven++;
        }
    }
    return counteven;
}
public static void main(String args[])
{
    Scanner sc=new Scanner(System.in);
    while(true)
    {
        System.out.println("enter the two numbers::");
        int fno=sc.nextInt();
        int sno=sc.nextInt();
        int noofeven=getEven(fno,sno);
        System.out.println("no of even numbers is: "+noofeven);
        System.out.println("continue:Y/N");
        String str=sc.nextLine(); //i simply input Y
        if(str.charAt(0)=='y')  //this line cause an exception
        break;
    }
}

}

output:::::::::::::::::::::

java Even

java Even

Process started >>>

enter the two numbers:: 1

10

no of even numbers is: 5

continue:Y/N

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0 at java.lang.String.charAt(Unknown Source) at Even.main(Even.java:27)

<<< Process finished. ================ READY ================