const MOD = 1_0000_0000_7
const HIGH = int32.high
proc scanf(formatstr: cstring){.header: "<stdio.h>", varargs.}
var n:int
scanf("%ld\n",addr n)
var res = 0
for _ in 0..<n:
  var c:int
  var d:int
  scanf("%ld %ld\n",addr c,addr d)
  c = (1 + (c-1) div 2)
  if c > HIGH : c = c mod MOD
  if d > HIGH : d = d mod MOD
  res += c * d
  if res > HIGH: res = res mod MOD
echo res