样例过了但只有20分，帮忙调一下谢谢！！！```cpp
#include<bits/stdc++.h>
#define N 500010
#define ll long long
using namespace std;
const int mod=1e9+7;
int n;
ll a[N],b[N],pa[N],pb[N],pab[N],ppa[N],ppb[N],ans=0;
int main() {
cin>>n;
for(int i=1;i<=n;i++){
cin>>a[i];
pa[i]=(pa[i-1]+a[i])%mod;
}
for(int i=1;i<=n;i++){
cin>>b[i];
pb[i]=(pb[i-1]+b[i])%mod;
}
for(int i=1;i<=n;i++){
pab[i]=(pab[i-1]+pa[i]pb[i])%mod;
ppa[i]=(ppa[i-1]+pa[i])%mod;
ppb[i]=(ppb[i-1]+pb[i])%mod;
}
for(int l=1;l<=n;l++){
ans+=(pab[n]-pab[l-1]-
pa[l-1](ppb[n]-ppb[l-1])-
pb[l-1]*(ppa[n]-ppa[l-1])+
(n-l+1)*pa[l-1]*pb[l-1])%mod;
}
cout<<ans%mod;
}
