POJ1990 MooFest

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<map>
#include<set>
using namespace std;
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define LL long long
#define CLR(x) memset(x,0,sizeof x)
#define MC(x,y) memcpy(x,y,sizeof(x))  
#define SZ(x) ((int)(x).size())
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1 
typedef pair<int,int> P;
const double eps=1e-9;
const int maxn=20010;
const int mod=1e9+7;
const int INF=1e9;

pair<LL,LL> p[maxn];
int n;
LL a,b;
LL Sum[maxn];
LL e[maxn],d[maxn];

int lowbit(int x){return x&-x;}

void add(int x,LL v,LL* c){
    while(x){
        c[x]+=v;
        x-=lowbit(x);
    }
}

LL sum(int x,LL* c){
    LL cnt=0;
    while(x<maxn){
        cnt+=c[x];
        x+=lowbit(x);
    }
    return cnt;
}

int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%lld%lld",&p[i].fs,&p[i].se);
    sort(p+1,p+n+1);
    for(int i=1;i<=n;i++) Sum[i]=Sum[i-1]+p[i].se;
    LL ans=0;
    add(p[1].se,p[1].se,e);
    add(p[1].se,1LL,d);
    for(int i=2;i<=n;i++){
        LL tmp=sum(p[i].se,e);//>=p[i].se
        LL num=sum(p[i].se,d);
        ans+=((i-1-num)*p[i].se-(Sum[i-1]-tmp)+tmp-num*p[i].se)*p[i].fs;
        add(p[i].se,p[i].se,e);
        add(p[i].se,1LL,d);
        //cout<<ans<<endl;
    }
    printf("%lld\n",ans);
    return 0;
}