问了jx，才看懂了题意。

#include <iostream>
#include <algorithm>
using namespace std;
struct data {
       int a,b;
}a[100010];
int t[100010],n;
__int64 ans;
bool cmp(data a,data b) {
     if (a.a<b.a) return true;
     else if (a.a==b.a && a.b<b.b) return true;
     return false;
}
void digui(int l,int r) {
     if (l==r) return;
     int mid = (l+r)>>1;
     digui(l,mid);
     digui(mid+1,r);
     int i=l,j=mid+1,k=l,p;
     while (i<=mid && j<=r) {
           if (a[i].b>a[j].b) {
                          ans+=mid-i+1;
                          t[k] = a[j].b;
                          j++;
           }
           else {
                t[k] = a[i].b;
                i++;
           }
           k++;
     }
     if (i==mid+1) for (p=j;p<=r;p++) t[k++] = a[p].b;
     else for (p=i;p<=mid;p++) t[k++] = a[p].b;
     for (k=l;k<=r;k++) a[k].b = t[k];
}
int main() {
    while (~scanf("%d",&n)) {
          for (int i=1;i<=n;i++)
              scanf("%d%d",&a[i].a,&a[i].b);
          sort(a+1,a+n+1,cmp);
          ans=0;
          digui(1,n);
          printf("%I64d\n",ans);
    }
    return 0;
}