#include <bits/stdc++.h> using namespace std; /* ------------------------Input Checker---------------------------------- */ long long readInt(long long l,long long r,char endd){ long long x=0; int cnt=0; int fi=-1; bool is_neg=false; while(true){ char g=getchar(); if(g=='-'){ assert(fi==-1); is_neg=true; continue; } if('0'<=g && g<='9'){ x*=10; x+=g-'0'; if(cnt==0){ fi=g-'0'; } cnt++; assert(fi!=0 || cnt==1); assert(fi!=0 || is_neg==false); assert(!(cnt>19 || ( cnt==19 && fi>1) )); } else if(g==endd){ if(is_neg){ x= -x; } if(!(l <= x && x <= r)) { cerr << l << ' ' << r << ' ' << x << '\n'; assert(1 == 0); } return x; } else { assert(false); } } } string readString(int l,int r,char endd){ string ret=""; int cnt=0; while(true){ char g=getchar(); assert(g!=-1); if(g==endd){ break; } cnt++; ret+=g; } assert(l<=cnt && cnt<=r); return ret; } long long readIntSp(long long l,long long r){ return readInt(l,r,' '); } long long readIntLn(long long l,long long r){ return readInt(l,r,'\n'); } string readStringLn(int l,int r){ return readString(l,r,'\n'); } string readStringSp(int l,int r){ return readString(l,r,' '); } /* ------------------------Main code starts here---------------------------------- */ const int MAX_T = 1e5; const int MAX_N = 1e5; const int MAX_SUM_LEN = 1e5; #define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0) #define ff first #define ss second #define mp make_pair #define ll long long #define rep(i,n) for(int i=0;i<n;i++) #define rev(i,n) for(int i=n;i>=0;i--) #define rep_a(i,a,n) for(int i=a;i<n;i++) #define pb push_back int sum_n = 0, sum_m = 0; int max_n = 0, max_m = 0; int yess = 0; int nos = 0; int total_ops = 0; ll mod = 1000000007; void solve() { int n = readIntLn(1, 1e5); sum_n += n; max_n = max(max_n, n); ll a[n], b[n]; rep(i,n){ if(i<n-1) a[i] = readIntSp(-1e14,1e14); else a[i] = readIntLn(-1e14, 1e14); } rep(i,n){ if(i<n-1) b[i] = readIntSp(-1e14,1e14); else b[i] = readIntLn(-1e14, 1e14); } rep(i,n) a[i] = b[i]-a[i]; ll ans = a[0]; ll curr = 1e15; int ok = 1; rev(i,n-2){ if(a[i]>a[i+1]) ok=2; if(a[i]<0 || a[i+1]<0) ok=0; } if(ok==1){ cout<<a[n-1]<<'\n'; return; } else if(ok==2) ok=1; rep(i,n){ if(!ok || a[i]<0 || (i>0 && a[i]<a[i-1])){ ok=0; break; } curr = min(curr, a[i]-(i>0?a[i-1]:0)); a[i]-=curr; } ans += a[n-1]; curr = 1e15; rev(i,n-1){ if(!ok || a[i]<0){ ok=0; break; } curr = min(curr, a[i]); a[i] -= curr; if(a[i]>0){ ok=0; break; } } if(ok) cout<<ans<<'\n'; else cout<<-1<<'\n'; } signed main() { #ifndef ONLINE_JUDGE freopen("input.txt", "r" , stdin); freopen("output.txt", "w" , stdout); #endif fast; int t = 1; t = readIntLn(1,10000); for(int i=1;i<=t;i++) { solve(); } assert(getchar() == -1); assert(sum_n<=2e5); cerr<<"SUCCESS\n"; cerr<<"Tests : " << t << '\n'; cerr<<"Sum of lengths : " << sum_n <<'\n'; cerr<<"Maximum length : " << max_n <<'\n'; // cerr<<"Total operations : " << total_ops << '\n'; //cerr<<"Answered yes : " << yess << '\n'; //cerr<<"Answered no : " << nos << '\n'; }