Thirti days has S_p_ _mb__, A_ _ _, _un_ and N_

Thirti days has S_p_ _mb__, A_ _ _, _un_ and N_ _e_b_ _.All the rest have thirti-one, Except for Fe_r_ _r_alone Which has twenty-eight days clear And twenty-nine days each lap year! Что необходимо вставлять заместо чертычек?(какие буквы)