n=int(input())
s=[*input()]
t=[*input()]
S=s[:]
T=t[:]
a=[]
ans=0
for i in range(n-2)[::2]:
    if s[i]==s[i+2]:
        if s[i+1]!=t[i+1]:
            s[i+1]=t[i+1]
            ans+=1
for i in range(1,n-2)[::2]:
    if s[i]==s[i+2]:
        if s[i+1]!=t[i+1]:
            s[i+1]=t[i+1]
            ans+=1
if s==t:a.append(ans)
ans=0
s=S[:]
t=T[:]
for i in range(1,n-2)[::2]:
    if s[i]==s[i+2]:
        if s[i+1]!=t[i+1]:
            s[i+1]=t[i+1]
            ans+=1
for i in range(n-2)[::2]:
    if s[i]==s[i+2]:
        if s[i+1]!=t[i+1]:
            s[i+1]=t[i+1]
            ans+=1
if s==t:a.append(ans)
if len(a)==0:print(-1)
else:print(min(a))