Jamie is walking along a number line that starts at point 0 and ends at point n. She can move either one step to the left or one step to the right of her current location , with the exception that she cannot move left from point 0 or right from point n. In other words, if Jamie is standing at point i,she can move to either i-1 or i+1 as long as her destination exists in the inclusive range [0,n]. She has a string ,s , of movement instruction consisting of the letters 1 and r , where 1 is an instruction to move one step left and r is an instruction to move one step right.

Jamie followed the instructions in s one by one and in order .For Example if s=‘rrlr’,she performs the following sequence of moves :one step right ->one step right ->one step left -> one step right .Jamie wants to move from point x to point y following some subsequence of string s instruction and wonders how many distinct possible subsequence of string s will get her from point x to point y. recall that a subsequence of a string is obtained by deleting zero or more characters from string .

it has four parameters

A String , s giving a sequence of eduction using the characters l( i.e. move left one unit ) and r (i.e. move right one unit)

An integer n, denoting the length of the number line.

An integer x, denoting jamie’s starting point on the number line

An integer y , denoting Jamie’s enidng point on the number line.

The function must return an integer denoting the total number of distinct subsequence of string s that will lead Jamie from point x to point y as this value cab be quite large .

Sample Input

rrlrlr

6

1

2

out put =7