#include <stdio.h>
#include <algorithm>
using namespace std;
struct Node
{
    int dps;
    int hp;
}a[30];
int cmp(Node x,Node y)
{
    return x.hp*y.dps<y.hp*x.dps;
}
int main()
{
    int t,i;
    int sum,ans;
    while(~scanf("%d",&t))
    {
        sum = ans = 0;
        for(i = 0;i<t;i++)
        {
            scanf("%d%d",&a[i].dps,&a[i].hp);
            sum+=a[i].dps;
        }
        sort(a,a+t,cmp);
        for(i = 0;i<t;i++)
        {
            ans+=sum*a[i].hp;
            sum-=a[i].dps;
        }
        printf("%d\n",ans);
    }
    return 0;
}