By looking at your error it seems that there are multiple class with the same name and selenium cannot locate it using ClassName.
Its better you try it using ID , Xpath or CSS Selector.
I used CSS Selector and it worked fine:
driver.findElement(By.cssSelector("#tsf > div:nth-child(2) > div > div.RNNXgb > div > div.a4bIc > input")).sendKeys("Hello World");
Hope it was of help.