#include<bits/stdc++.h>
using namespace std;
#define N 100010
int n,ans,cnt,top,num=0;
int s[N];
struct email
{
    int x,y;
}a[N];
inline void read(int &x)
{
    x=0;int f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    x*=f;
}

bool cmp(email a,email b)
{
    return a.y<b.y;
}

int main()
{
    read(n);
    for(int i=1;i<=n;i++)
    {
        int x,y;
        read(x);read(y);
        if(x<0||y<0)continue;
        a[++cnt].x=x;a[cnt].y=y;
    }
    sort(a+1,a+1+cnt,cmp);
    for(int i=1;i<=cnt;i++)
    {
        if(a[i].x>=s[top])s[++top]=a[i].x;
        else
        {
            int pos=lower_bound(s+1,s+1+top,a[i].x)-s;
            s[pos]=a[i].x;
        }
    }
    printf("%d
",top);
    return 0;
}