You are given two 0-indexed strings source and target, both of length n and consisting of lowercase English letters. You are also given two 0-indexed character arrays original and changed, and an integer array cost, where cost[i] represents the cost of changing the character original[i] to the character changed[i]. You start with the string source. In one operation, you can pick a character x from the string and change it to the character y at a cost of z if there exists any index j such that cost[j] == z, original[j] == x, and changed[j] == y. Return the minimum cost to convert the string source to the string target using any number of operations. If it is impossible to convert source to target, return -1. Note that there may exist indices i, j such that original[j] == original[i] and changed[j] == changed[i].