#include<cstdio>
long long a[100005];
long long b[100005];

long long min(long long a,long long b){ return a>b?b:a; }

int main(){
    int n;
    scanf("%d",&n);
    long long sumA = 0, sumB = 0;
    for(int i = 1; i <= n; i++){
        scanf("%lld",&a[i]);
        sumA += a[i];
    }
    for(int i = 1; i <= n; i++){
        scanf("%lld",&b[i]);
        sumB += b[i];
    }
    long long add = 2-n, diff = sumB-sumA;
    if(n==2){
        if(diff!=0) printf("-1\n");
        else{
            long long gap = a[1]-b[1];
            if(gap<0) gap *= -1;
            printf("%lld\n",gap);
        }
    }
    else if(diff%add || diff>0) printf("-1\n");
    else{
        long long time = diff/add;
        long long have = time*2;
        int ok = 1;
        for(int i = 1; i <= n; i++){
            a[i] -= time;
            //printf("a[%d] = %lld\n",i,a[i]);
            if(a[i]>b[i]) ok = 0;
            else{
                long long gap = b[i]-a[i];
                if(gap%2 || gap>have) ok = 0;
                else have -= gap;
            }
        }
        if(ok) printf("%lld\n",time);
        else printf("-1\n");
    }
    return 0;
}