Approval Workflow

I have a requirement for custom three level approval.  where first level is manager, second level is role admin and third is dept head.  Of this when first level approves the request it goes to second level. My requirement is here where and when the request goes to second level the approver should have only option which is approve by entering a comment. Which means at second level approval reject option should not be visible for the approver and third level he can either approve or reject the request.

Please any one can help me how we can acheive this.