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



int main(int argc, char *argv[])
{

	int N = 0;
	scanf("%u", &N);

	unsigned long long lC = 0;
	unsigned long long lD = 0;
	unsigned long long lE = 0;

	for (int i = 0; i < N; i++)
	{
		scanf("%llu %llu", &lC, &lD);

		if (lC == 1 || lC == 2)
			lE += lD;
		else
		{
			if (lC % 2 == 0)
				lE += ( lC / 2 ) * lD;
			else
				lE += ( lC / 2 + 1 ) * lD;
		}
	}
	if( lE > 1000000000 )
		printf("%llu\n", lE % 1000000000 + 7);
	else
		printf("%llu\n", lE);

	return 0;

}