numbering names

Hi. I have a column of data with names in it. for example john smith I need excel to number the names so for example john smith produces a 1 in the next column and then each time john smith comes up the next column adds a number to 1

so it would look like this

john smith 1
john smith 2
john smith 3

when the name changes the process would start again. If the next name was jane smith it would produce

jane smith 1
jane smith 2
jane smith 3