#include<bits/stdc++.h>
using namespace std;

typedef pair<int,int> pa;
const int MAXN=1e6+5;
struct node
{
    int x,y;
}p[MAXN];
vector<pa>X[MAXN],Y[MAXN];
int numx[MAXN],numy[MAXN],ans[MAXN];
int n,lenx,leny;
namespace debug{
    int vis[500][500];
    vector<node> cntx[MAXN], cnty[MAXN];
    int check(int ans[]){
        for(int i = 1; i <= n; i++){
            if(ans[i] == 1){
                cntx[p[i].x].push_back(p[i]);
                cnty[p[i].y].push_back(p[i]);
            }
        }
        for(int i = 1; i <= lenx; i++) if((int)cntx[i].size() > 2) return i;
        for(int i = 1; i <= leny; i++) if((int)cnty[i].size() > 2) return i;
        for(int i = 1; i <= n; i++){
            if(ans[i] == 1) continue;
            if(cnty[p[i].y].size() == 2){
                int x1 = cnty[p[i].y][0].x, x2 = cnty[p[i].y][1].x;
                if(x1 > x2) swap(x1, x2);
                if(x1 < p[i].x && x2 > p[i].x) continue;
            }
            if(cntx[p[i].x].size() == 2){
                int y1 = cntx[p[i].x][0].y, y2 = cntx[p[i].x][1].y;
                if(y1 > y2) swap(y1, y2);
                if(y1 < p[i].y && y2 > p[i].y) continue;
            }
            return -1;
        }
        return 0;
    }
    void main(int ans[]){
        printf("%d\n",check(ans));
    }
    void print(int ans[]){
        printf("--------------------------\n");
        for(int i = 1; i <= n; i++) printf("%d %d\n",p[i].x,p[i].y);
        printf("\n");
        for(int i = 1; i <= n; i++){
            if(ans[i] == 0) vis[p[i].x][p[i].y] = 1;
            else vis[p[i].x][p[i].y] = 2, printf("%d %d\n",p[i].x,p[i].y);
        }
        printf("\n");
        for(int i = 1; i <= lenx; i++){
            for(int j = 1; j <= leny; j++) printf("%d ",vis[i][j]);
            printf("\n");
        }
    }
}
int main()
{
    //freopen("tower4.in","r",stdin);
    //freopen("tower.out","w",stdout);
    cin>>n;
    for(int i=1;i<=n;++i) scanf("%d %d",&p[i].x,&p[i].y),numx[i]=p[i].x,numy[i]=p[i].y;
    sort(numx+1,numx+n+1),sort(numy+1,numy+n+1);
    lenx=unique(numx+1,numx+n+1)-numx-1,leny=unique(numy+1,numy+n+1)-numy-1;
    for(int i=1;i<=n;++i)
    {
        p[i].x=lower_bound(numx+1,numx+lenx+1,p[i].x)-numx;
        p[i].y=lower_bound(numy+1,numy+leny+1,p[i].y)-numy;
        //printf("%d %d\n",p[i].x,p[i].y);
    }
    //return 0;
    for(int i=1;i<=n;++i) X[p[i].x].push_back({p[i].y,i});
    for(int i=1;i<=lenx;++i)
    {
        sort(X[i].begin(),X[i].end());
        int si=X[i].size();
        Y[X[i][0].first].push_back({i,X[i][0].second});
        if(si>=2) Y[X[i][si-1].first].push_back({i,X[i][si-1].second});
    }
    for(int i=leny;i>=1;--i)
    {
        if(Y[i].size()<=2)
        {
            for(auto j:Y[i]) ans[j.second]=1;
            continue;
        }
        sort(Y[i].begin(),Y[i].end());
        int si=Y[i].size();
        ans[Y[i][0].second]=ans[Y[i][si-1].second]=1;
        vector<pa>tmp;
        tmp.push_back(Y[i][0]);
        if(si>=2) tmp.push_back(Y[i][si-1]);
        for(int j=1;j<si-1;++j)
        {
            ans[Y[i][j].second]=0;
            pa now={i,Y[i][j].second};
            int pos=lower_bound(X[Y[i][j].first].begin(),X[Y[i][j].first].end(),now)-X[Y[i][j].first].begin()-1;
            if(pos>0) Y[X[Y[i][j].first][pos].first].push_back({Y[i][j].first,X[Y[i][j].first][pos].second});
            else tmp.push_back(Y[i][j]);
        }
        Y[i]=tmp;
    }
    for(int i=1;i<=leny;++i)
    {
        if(Y[i].size()<=2)
        {
            for(auto j:Y[i]) ans[j.second]=1;
            continue;
        }
        sort(Y[i].begin(),Y[i].end());
        Y[i].erase(unique(Y[i].begin(),Y[i].end()),Y[i].end());
        int si=Y[i].size();
        ans[Y[i][0].second]=ans[Y[i][si-1].second]=1;
        /*if(i==4){
        cout<<"!!!"<<endl;
        for(auto [x,y]:Y[i]) printf("%d %d\n",x,y);
        return 0;
        }*/
        //vector<pa>tmp;
        //tmp.push_back(Y[i][0]),tmp.push_back(Y[i][si-1]);
        for(int j=1;j<si-1;++j)
        {
            ans[Y[i][j].second]=0;
            pa now={i,Y[i][j].second};
            int pos=upper_bound(X[Y[i][j].first].begin(),X[Y[i][j].first].end(),now)-X[Y[i][j].first].begin();
            if(pos<X[Y[i][j].first].size()-1) Y[X[Y[i][j].first][pos].first].push_back({Y[i][j].first,X[Y[i][j].first][pos].second});
            //else tmp.push_back(Y[i][j]);
        }
        //Y[i]=tmp;
    }
    //for(int i=1;i<=n;++i) if(ans[i]) putchar(i+'A'-1);
    //debug::main(ans);
    //for(int i=1;i<=n;++i) printf("%d",ans[i]);
    return 0;
}