B'Naman has two binary strings s and t of length n (a binary string is a string which only consists of the characters "0" and "1"). He wants to convert s into t using the following operation as few times as possible. In one operation, he can choose any subsequence of s and rotate it clockwise once. For example, if s = 1 textbf{1}101 textbf{00} , he can choose a subsequence corresponding to indices ( 1 -based) {2, 6, 7 } and rotate them clockwise. The resulting string would then be s = 1 textbf{0}101 textbf{10} . A string a is said to be a subsequence of string b if a can be obtained from b by deleting some characters without changing the ordering of the remaining characters. To perform a clockwise rotation on a sequence c of size k is to perform an operation which sets c_1:=c_k, c_2:=c_1, c_3:=c_2, ldots, c_k:=c_{k-1} simultaneously. Determine the minimum number of operations Naman has to perform to convert s into t or say that it is impossible. The first line contains a single integer n (1 <= n <= 10^6) -- the length of the strings. The second line contains the binary string s of length n . The third line contains the binary string t of length n . If it is impossible to convert s to t after any number of operations, print -1 . Otherwise, print the minimum number of operations required. In the first test, Naman can choose the subsequence corresponding to indices {2, 6 } and rotate it once to convert s into t . In the second test, he can rotate the subsequence corresponding to all indices 5 times. It can be proved, that it is the minimum required number of operations. In the last test, it is impossible to convert s into t . '...