#include <algorithm>

#include <cstdio>

using namespace std;

struct node

{

    int Line,T;

    bool operator<(node a)const

    {

        if(a.Line==Line) return T<a.T;

        else return Line<a.Line;

    }

}zombie[];

int n;

int main()

{

    scanf("%d",&n);

    int Answer=,Maxn;

    for(int i=;i<=n;i++)

    {

        scanf("%d%d",&zombie[i].Line,&zombie[i].T);

        Maxn=max(Maxn,zombie[i].T);

    }

    sort(zombie+,zombie++n);

    int i=;

    while(i<=n)

    {

        int pos=zombie[i].Line,T_now=zombie[i].T-;

        while(T_now<=Maxn)

        {

            T_now+=;

            while(zombie[++i].Line==pos&&zombie[i].T<=T_now);

            if(zombie[i].Line!=pos) {Answer++;break;}

            if(zombie[i].T>T_now) {Answer++;break;}

        }

    }

    printf("%d",Answer);

    return ;

}