#include <stdio.h>
int main(void){
	int N;			//	机の種類
	int C,D;		//	C：椅子の個数、D：同じ種類の机の個数
	long int capacity = 0;
	
	scanf("%d",&N);
	
	for(int i = 0; i < N; i++){
		scanf("%d %d",&C,&D);
		if(C % 2 != 0){
			C /= 2;
			C++;
		}else{
			C /= 2;
		}
		capacity += (C*D)%1000000007;
		capacity %= 1000000007;
	}
	
	printf("%ld\n",capacity);
	return 0;
}