Partying with Babu Bhai

Problem description: As babu bhai has won the ACM ICPC world final by solving the last above question. Now he and his team mates are going for a party at a bar. After the party there are n baatleys left. Each baatley is described by two values i.e. the reamaining amount of beer (ai) and the volume of that baatley(bi). As babu bahiya want to carry the minimum number of remaining baatley with him.