[c#] Add zero-padding to a string

How do I add "0" padding to a string so that my string length is always 4?

Example

If input "1", 3 padding is added = 0001
If input "25", 2 padding is added = 0025
If input "301", 1 padding is added = 0301
If input "4501", 0 padding is added = 4501

int num = 1;
num.ToString("0000");

string strvalue="11".PadRight(4, '0');

output= 1100

string strvalue="301".PadRight(4, '0');

output= 3010

string strvalue="11".PadLeft(4, '0');

output= 0011

string strvalue="301".PadLeft(4, '0');

output= 0301

"1".PadLeft(4, '0');

myInt.ToString("D4");