Problem Statement

There is a string S of length N consisting of characters 0 and 1. You will perform the following operation for each i = 1, 2, ..., m:

• Arbitrarily permute the characters within the substring of S starting at the l_i-th character from the left and extending through the r_i-th character.

Here, the sequence l_i is non-decreasing.
How many values are possible for S after the M operations, modulo 1000000007(= 10^9+7)?

Input

The input is given from Standard Input in the following format:
N M
S
l_1 r_1
:
l_M r_M

Output

Print the number of the possible values for S after the M operations, modulo 1000000007.

Constraints

• 2≦N≦3000
• 1≦M≦3000
• S consists of characters 0 and 1.
• The length of S equals N.
• 1≦l_i < r_i≦N
• l_i ≦ l_{i+1}

Sample Input 1

5 2
01001
2 4
3 5

Sample Output 1

6

After the first operation, S can be one of the following three: 01001, 00101 and 00011.
After the second operation, S can be one of the following six: 01100, 01010, 01001, 00011, 00101 and 00110.

Sample Input 2

9 3
110111110
1 4
4 6
6 9

Sample Output 2

26

Sample Input 3

11 6
00101000110
2 4
2 3
4 7
5 6
6 10
10 11

Sample Output 3

143

见题面 Input 部分

见题面 Output 部分