import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv;
import std.numeric, std.math, std.bigint, std.bitmanip, std.random;
import std.stdio, std.typecons;

const auto mod = 10 ^^ 9 + 7;

void main()
{
  auto n = readln.chomp.to!long;
  auto cdi = iota(n)
    .map!(_ => readln.split.map!(to!long))
    .map!(rd => tuple(rd[0], rd[1]));

  auto r = 0;
  foreach (cd; cdi) {
    auto a = (cd[0] / 2 + (cd[0] % 2 == 0 ? 0 : 1)) % mod;
    auto b = cd[1] % mod;
    r = (r + (a * b) % mod) % mod;
  }

  writeln(r);
}