n=int(input())
a=list(map(int,input().split()))
b=list(map(int,input().split()))

ans=0
for x in range(n):
    c=b[x]-a[x]
    ans+=c
    
if n==2:
    if a[0]-b[0]==-1*(a[1]-b[0]):
        print(abs(a[0]-b[0]))
    else:
        print(-1)
        
else:
    if ans%(2-n)==0:
        ans1=ans//(2-n)
        ch=0
        out=0
        for u in range(n):
            e=b[u]-a[u]
            if (e+ans1)%2==1:
                out+=1
            ch+=(e+ans1)//2
        
        if out==0 and ch==ans1:
            print(ans1)
        else:
            print(-1)
    else:
        print(-1)