/** @file 754.cpp @title No.754 畳み込みの和 - yukicoder @url https://yukicoder.me/problems/no/754 **/ #include using namespace std; typedef long long LL; typedef unsigned long long uLL; #define ALL(obj) (obj).begin(), (obj).end() #define RALL(x) (x).rbegin(), (x).rend() #define SZ(x) ((int)(x).size()) #define REPI(i, a, b) for (LL i = LL(a); i < LL(b); ++i) #define REP(i, N) for (LL i = LL(0); i < LL(N); ++i) #define REPS(i, N) for (int i = 1; i <= (int)(N); i++) #define RREP(i, N) for (int i = ((int)(N)-1); i >= 0; i--) #define RREPS(i, N) for (int i = ((int)(N)); i > 0; i--) #define chmax(ret, x) ret = max(ret, x) #define chmin(ret, x) ret = min(ret, x) #define FILL(x, e) memset(x, e, sizeof(x)) #define ZEROS(x) fill(x, 0) #define SORT(x) sort(ALL(x)) #define RSORT(x) sort(RALL(x)) #define UNIQ(x) x.erase(unique(ALL(x)), x.end()) #define BIT(n) (1LL << (n)) #define OUT(x) cout << (x) << "\n" #define DEBUG(x) cerr << #x << " : " << x << "\n" #define DEBUG2(x, y) cerr << "(" << #x << ", " << #y << ") = (" << x << ", " << y << ")\n"; #define PB push_back #define EB emplace_back #define MP make_pair #define MT make_tuple #define FI first #define SE second const int MOD = 1e9 + 7; void iostream_init() { ios::sync_with_stdio(false); cin.tie(0); cout.setf(ios::fixed); cout.precision(12); // cout.fill('0'); // cout.width(3); } int main() { ::iostream_init(); int N; cin >> N; vector a(N + 1, 0); vector b(N + 1, 0); REP(i, N + 1) { cin >> a[i]; } REP(i, N + 1) { cin >> b[i]; } // naive solution // LL c = 0L; // REP(i, N + 1) { // REP(j, i + 1) { // c += (a[j] * b[i - j]) % MOD; // } // c %= MOD; // } // OUT(c % MOD); vector bsm(N + 1, b[0]); REPI(i, 1, N + 1) { bsm[i] = (bsm[i - 1] + b[i]) % MOD; } LL ans = 0; REP(i, N + 1) { ans += (a[i] * bsm[N - i]) % MOD; } OUT(ans % MOD); return 0; }