Monsters vs you : an optimisation puzzle

You are attacked by a set of N monsters in a game. You have to design an algorithm to calculate the maximum number of these you could kill, adhering to the constraints below.

You begin with B units of initial energy.
To kill a monster n (1<=n<=N), you need to spend Kn units of energy out of your reserve. After it is killed, you gain Gn units of energy in return.
At any point, if you do not have sufficient energy left to attack any of the remaining monsters, you stop at that point.

INPUT : 
B 
N 
K1 G1 
K2 G2 
. 
. 
KN GN
Where

B = initial energy you being with(B<100)
N = total number of monsters (N<10000) followed by N lines in the form
Kn Gn = Kn is energy needed to kill monster n(1<=n<=N) and Gn is energy gained after killing monster n(1<=n<=N) These N lines for the K and G values are not sorted in anyway, i.e neither on ASC/DESC order of K, nor on G.

OUTPUT : 
M = maximum number of monsters that can be killed

Provide a Java implementation of the method below (any other language or pseudocode also works)

public static int maxMonsters(int B, int [][] KG) {
  int M = 0;
  //KG is guaranteed to be of length N, KG[n][0] KG[n][1] are Kn and Gn for monster n
  //your implementation goes here
  return M;
}