Nguồn: http://codeforces.com
Kirito is stuck on a level of the MMORPG he is playing now. To
move on in the game, he's got to defeat all n dragons
that live on this level. Kirito and the dragons have strength,
which is represented by an integer. In the duel between two opponents the
duel's outcome is determined by their strength. Initially, Kirito's strength
equals s.
If Kirito starts duelling with the i-th (1 ≤ i ≤ n) dragon and
Kirito's strength is not greater than the dragon's strength xi, then Kirito
loses the duel and dies. But if Kirito's strength is greater than the dragon's
strength, then he defeats the dragon and gets a bonus strength increase by yi.
Kirito can fight the dragons in any order. Determine whether he
can move on to the next level of the game, that is, defeat all dragons without
a single loss.
Input
The first line contains two space-separated integers s and n (1 ≤ s ≤ 104, 1 ≤ n ≤ 103). Then n lines
follow: the i-th line contains space-separated integers xi and yi (1 ≤ xi ≤ 104, 0 ≤ yi ≤ 104) — the i-th dragon's
strength and the bonus for defeating it.
Output
On a single line print "YES" (without
the quotes), if Kirito can move on to the next level and print "NO" (without
the quotes), if he can't.
Examples
input
2 2
1 99
100 0
1 99
100 0
output
YES
input
10 1
100 100
100 100
output
NO
Note
In the first sample Kirito's strength initially equals 2. As the
first dragon's strength is less than 2, Kirito can fight it and defeat it.
After that he gets the bonus and his strength increases to 2 + 99 = 101. Now he can
defeat the second dragon and move on to the next level.
In the second sample Kirito's strength is too small to defeat
the only dragon and win.
Tóm tắt đề:
_ Để thắng
được vòng tiếp theo, Kirito cần hạ được n con rồng. Ban đầu, Kirito có chỉ số sức
mạnh là s.
_ Nếu sức
mạnh hiện tại của Kirito mạnh hơn sức mạnh x[i] của con rồng, thì Kirito sẽ
đánh bại được con rồng và tăng thêm được 1 lượng sức mạnh là y[i]. Ngược lại,
Kirito sẽ chết.
_ Hỏi :
Kirito có đến được vòng tiếp theo hay không ?
Solution by ĐNK