# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = int(input())
	ans = 0
	for i in range(N):
		C, D = getlist()
		ans += (int((C + 1) // 2) * D) % con

	ans %= con
	print(ans) 

if __name__ == '__main__':
	main()