N = int(input())
S = input()
T = input()

if S[0] != T[0] or S[-1] != T[-1]:
    exit(print(-1))

def func(S):
    ans = []
    for i in range(N-1):
        ans.append(0 if S[i] == S[i+1] else 1)
        if i%2 == 1:
            ans[i] ^= 1
    return ans

def func2(A):
    ans = []
    for i in range(len(A)):
        if A[i] == 1:
            ans.append(i)
    return ans

A = func(S)
B = func(T)
if A.count(1) == B.count(1):
    idxA = func2(A)
    idxB = func2(B)
    ans = 0
    for i in range(len(idxA)):
        ans += abs(idxA[i]-idxB[i])
    print(ans)
else:
    print(-1)