S1, S2, S3, and S4 rented the apartment of Michi for a period of one year. After one semester, S1, S2, and S3 returned to their home country and S4 transferred to a boarding house. Michi discovered that they left unpaid telephone bills in the total amount of P40, 000.00. The lease contract provided that the lessees shall pay for the telephone services in the leased premises. Michi demanded that S4 should pay the entire amount of the unpaid telephone bills, but the latter is willing to pay only one fourth of it. Is S4's contention correct? Why?