n=int(input())
s=input()
t=input()
if s[0]!=t[0] or s[-1]!=t[-1]:
  print(-1)
  exit()

a=[]
b=[]
for i in range(n-1):
  if (s[i]!=s[i+1])^(i%2):
    a.append(i)
  if (t[i]!=t[i+1])^(i%2):
    b.append(i)

if len(a)!=len(b):
  print(-1)
  exit()

ans=0
for i in range(len(a)):
  ans+=abs(a[i]-b[i])

print(ans)