●POJ 1990 MooFest

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define MAXN 20050
#define abs(x) (x<0?-x:x)
using namespace std;
struct Pii{
	int a,b;
	Pii(int _a=0,int _b=0):a(_a),b(_b){}
	bool operator < (const Pii &rtm)const{return b<rtm.b;}
	void operator += (const Pii &rtm){a+=rtm.a; b+=rtm.b;};
}cow[MAXN];
struct BIT{
	int N; Pii A[MAXN];
	int Lowbit(int x){return x&-x;}
	void Reset(int n){N=n; memset(A,0,sizeof(A));}
	void Modify(int p,Pii w){
		while(p<=N) A[p]+=w,p+=Lowbit(p);
	}
	Pii Query(int p){
		static Pii ret; ret.a=ret.b=0; 
		while(p) ret+=A[p],p-=Lowbit(p);
		return ret;
	}
}DT;
int main(){
	int n; scanf("%d",&n);
	Pii tmp; long long ans=0;
	for(int i=1;i<=n;i++) scanf("%d%d",&cow[i].a,&cow[i].b);
	sort(cow+1,cow+n+1);
	for(int k=0;k<=1;k++){
		DT.Reset(20000);
		if(k==1) reverse(cow+1,cow+n+1);
		for(int i=1;i<=n;i++){
			tmp=DT.Query(cow[i].a-k);
			ans+=1ll*abs((tmp.b*cow[i].b-tmp.a))*cow[i].a;
			DT.Modify(cow[i].a,Pii(cow[i].b,1));
		}
	}
	printf("%lld\n",ans);
	return 0;
}