Er. Gangaram told you how to fix your code.
I just wanted to give a short explainer. ;)
input returns a string, a text. When you do a + b and both of them are strings, then the result is a string concatenation, that is, putting the strings after one another. This is why your result is "3" + "4" = "34", a string.
If you want to treat your values as integral numbers, you need to cast them to int (as per Er. Gangaram suggested). Now, you will get the classic mathematical results, the sum of two integral numbers: 3 + 4 = 7, i.e., an integral number.