You have been given $n$ characters $a_0, a_1, a_2, \ldots, a_n$. They are arranged in their lexicographical value, i.e. $a_0 < a_1 < a_2 < a_3 < \ldots < a_n$. Now, you have to determine the number of all the strings of length $n = 2702$ such that for every character equal to $a_k$ in the string , $a_k+1,a_k+2,a_k+3.... , a_n$ must appear before it at least once.

Answer the value as modulo $1000000007$ .

Note that it is not necessary to use all the characters in a string.