Excel - need to copy a value from one column to another, if the original value exists in a different column

I dont normally program in excel but I need to right now. I need to check if cell A1 is in another column (Column n for example) and if it is, get the cell value of the corresponding row number, in the column to the right of Column N (Column O). and lets say the formula is placed into column P. and if the number cannot be found in column n, put a piece of text such as 'not found'.

Column A             Column N     Column O       Column P
1000                 1000           4556           4556
1001                 1005           4777           not found
1002                 1003           4578           not found
1003                 1007           1111           4578

1001 and 1002 are not found in column n so they get 'not found' the other 2 would be found and get the corresponding values from column O. How can I write this in excel code?