import std.stdio;
import std.string;
import std.conv;
import std.algorithm;
import std.array;
import std.range;
import std.typecons;

/// main ==================
void main()
{
  auto MOD = 1_000_000_007;
  long people;
  auto N = readln.strip.to!int;
  foreach(n; 0..N)
  {
    auto buf = readln.strip.split;
    long Ck = buf[0].to!long % MOD;
    long Dk = buf[1].to!long % MOD;
    auto add = (Ck + 1) / 2 * Dk;
    people += add;
    people %= MOD;
  }
  people.writeln;
}