How to Login and Logout in Gmail

import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.firefox.FirefoxDriver;

public class Openbrowser
{
public static void main(String args[]) throws InterruptedException
{
WebDriver driver=new FirefoxDriver();
driver.manage().timeouts().implicitlyWait(30,TimeUnit.SECONDS);
driver.get("http://gmail.com/");
driver.findElement(By.id("Email")).sendKeys("raghav@mobikwik.com");
driver.findElement(By.id("Passwd")).sendKeys("9910979218");
driver.findElement(By.id("signIn")).click();
Thread.sleep(4000);
driver.findElement(By.xpath("//*[@id='gb']/div[1]/div[1]/div[2]/div[5]/div[1]/a/span")).click();
driver.findElement(By.id("gb_71")).click();
}
}