#include <stdio.h>

int main(void) {
	int i, N;
	long long int C, D, sum;
	scanf("%d", &N);
	sum = 0;
	for(i = 1;i <= N;i++){
		scanf("%lld%lld", &C, &D);
		sum += (((C + 1) / 2) * D) % 1000000007;
		sum %= 1000000007;
	}
	printf("%lld\n", sum);
	
	return 0;
}