/** @file 146.cpp @title No.146 試験監督(1) - yukicoder @url https://yukicoder.me/problems/no/146 **/ #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; uLL C, D; uLL ans = 0; REP(i, N) { cin >> C >> D; C = C % 2 == 0 ? C / 2 : (C + 1) / 2; ans += ((C)*D) % MOD; } OUT(ans % MOD); return 0; }