by hansang:

#include<bits/stdc++.h>
using namespace std;
const int N=1010;
int a[N], b[N], mp[N];
int main(){
    int n, ans=0; scanf("%d", &n);
    for(int i=1; i<=n; i++){
        scanf("%d%d", &a[i], &b[i]);
        mp[a[i]] = i;
    }
    for(int i=1; i<=n; i++){
        for(int j=i+1; j<=n; j++){
            if(mp[b[i]] > mp[b[j]]) ans++;
        }
    }
    printf("%d\n", ans);
    return 0;
}

by hansang:

#include<bits/stdc++.h>
using namespace std;
const int N=1010;
int a[N], b[N], mp[N];
int main(){
	int n, ans=0; scanf("%d", &n);
	for(int i=1; i<=n; i++){
		scanf("%d%d", &a[i], &b[i]);
		mp[a[i]]=i;
	}
	for(int i=1; i<=n; i++){
		for(int j=i+1; j<=n; j++){
			if(mp[b[i]]>mp[b[j]]) ans++;
		}
	}
	printf("%d\n", ans);
	return 0;
}