Decompression

You are given a character string S of length N (1-indexed) and an array x of N integers. Now, you want to form a new string R as follows. For each position i in the array x, you pick an integer k uniformly randomly from range 1 to x[i] and repeat the character S[i], k times in R. You have to find the expected (average) length of decompressed string. Input First line of the input contains an int