// yukicoder: No.146 試験監督（1）
// 2019.4.11 bal4u

#include <stdio.h>
#include <stdlib.h>

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif
long long in()
{
	int c = gc();
	long long n = 0;
	do n = 10 * n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

#define M 1000000007

int main()
{
	int N;
	long long c, d, ans;

	N = (int)in();
	ans = 0;
	while (N--) {
		c = ((in()+1)>>1) % M, d = in() % M;
		ans += (c * d) % M;
	}
	printf("%d\n", (int)(ans % M));
	return 0;
}