import sequtils,strutils
var
    N = stdin.readline.parseInt
    d,c,ans : int64
    m : int64 = 1_000_000_007
for n in 1..N:
    (c, d) = stdin.readline.split.map(parseBiggestInt)
    ans = (ans + (d * ((c + 1) div 2))) mod m
echo ans