按照结束时间从早到晚看，要是当前时间小于开始时间，则可以看。每次看完时间变为结束时间。

#include <iostream>
#include <cstdio>
#include <algorithm>

using namespace std;

struct Program{
    int start;
    int end;
}; 

Program programs[101];

bool cmp(Program a, Program b){
    return a.end < b.end;
}

int main(){
    int n;
    int ans, now; 
    while (cin >> n) {
        if(n == 0) break; 
        ans = 0;
        now = 0;
        for(int i = 0; i < n; i++){
            cin >> programs[i].start >> programs[i].end;
        }
        sort(programs, programs + n, cmp);
//        for(int i = 0; i < n; i++){
//            cout << programs[i].end << endl;
//        }
        for(int i = 0; i < n; i++){
            if(now <= programs[i].start){
                //cout << programs[i].start << endl;
                now = programs[i].end;
                ans++;
            }
        }
        cout << ans << endl;
    }
    return 0; 
}