POJ 3362 Protecting the Flowers

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

const int maxn=100000+10;
struct X
{
    long long t;
    long long d;
} s[maxn];
int n;

bool cmp(const X&a,const X&b)
{
    return a.t*b.d<b.t*a.d;
}

int main()
{
    while(~scanf("%d",&n))
    {
        for(int i=1; i<=n; i++) scanf("%lld%lld",&s[i].t,&s[i].d);
        sort(s+1,s+1+n,cmp);
        long long ans=0;
        long long sum=2*s[1].t;
        for(int i=2; i<=n; i++)
        {
            ans=ans+s[i].d*sum;
            sum=sum+2*s[i].t;
        }
        printf("%lld\n",ans);
    }
    return 0;
}