区间合并：

#include <bits/stdc++.h>

using namespace std;
typedef pair <int,int> pii;
vector<pii>pos;
void merge(vector<pii>&pos)
{
    vector <pii>ans;
    sort(pos.begin(),pos.end());
    int st=-1e9+10,ed=-1e9+10;
    for (auto ver:pos)
    {
        if (ed<ver.first)
        {
            if (st!=-1e9+10)ans.push_back({st,ed});
            st=ver.first,ed=ver.second;
        }
        else
        {
            ed=max(ed,ver.second);
        }
    }
    if (st!=-1e9+10)ans.push_back({st,ed});
    pos=ans;
}
int main()
{
    int n;
    cin>>n;
    while (n--)
    {
        int l,r;
        cin>>l>>r;
        pos.push_back({l,r});
    }
    merge(pos);
    cout<<pos.size()<<endl;
    //for (auto ver:pos)cout<<ver.first<<' '<<ver.second<<endl;
    return 0;
}