#include<bits/stdc++.h>
using namespace std;
int n;
const int N=100005;
int a[N*2];
vector<int> f[N*2];
int getans(int l,int r)
{
    for (int i=0;i<(int)f[r].size();++i)
        if (l>f[r][i])
            return i;
    return f[r].size();
}
int main()
{
    scanf("%d",&n);
    for (int i=1,u,v;i<=n;++i)
    {
        scanf("%d%d",&u,&v);
        a[v]=u;
    }
    for (int i=2;i<=n*2;++i)
    {
        f[i]=f[i-1];
        if (!a[i])
            continue;
        int p=getans(i-1,a[i]+1);
        if (p+f[a[i]-1].size()+1>f[i].size())
            f[i].resize(p+f[a[i]-1].size()+1,-1);
        f[i][p]=max(f[i][p],a[i]);
        for (int j=0;j<f[a[i]-1].size();++j)
            f[i][p+j+1]=max(f[i][p+j+1],f[a[i]-1][j]);
    }
    printf("%d\n",(int)f[n*2].size());
    return 0;
}