Add validation for "Average views per month" field

[veronicamacovei]

Website Page - https://www.adtechmedia.io/calculator/

Average views per month field
Actual result: This field is valid when I insert:

• ‘e’ letter
• Special characters ‘-’ and ‘+’
• An unlimited number of digits
• 

Expected result :

• Only integer
• Only Numbers
• Min value 1
• No special characters like '-', '+' , 'e', '.'