//贪心,开始的时候直接按Dps排序,w了
#include<iostream>
#include<algorithm>
using namespace std;
struct A
{
int a, b;
}run[25];
bool cmp(A c, A d)
{
if((double)c.b/c.a == (double)d.b/d.a)
return c.a < d.a;
else
return (double)c.b/c.a > (double)d.b/d.a;
}
int main()
{
int n;
while(scanf("%d", &n) != EOF)
{
int i;
for( i=0; i < n; i++ )
scanf("%d%d", &run[i].a, &run[i].b);
sort(run, run+n, cmp);
int t = 0, s = 0;
for( i=0; i < n; i++ )
{
s += (t+run[i].a) * run[i].b;
t += run[i].a;
}
printf("%d\n", s);
}
return 0;
}