为什么暴力这样写只有 40 分？

#include<bits/stdc++.h>
#define int1 long long
using namespace std;
int1 n,m,a[1005],b[1005],i,j,s;
bool c[1005];
int main(){
    cin >> n >> m;
    for(i = 1; i <= m; i++){
        cin >> a[i] >> b[i];
    }
    for(i = 1; i <= m; i++){
        for(j = i + 1; j <= m; j++){
            if(a[i] >= a[j] && b[i] <= b[j] && i != j){
                c[i] = 1;
            }
        }
    }
    for(i = 1; i <= m; i++){
        s += (!c[i]);
        /*if(!c[i]){
            cout<< i << endl;
        }*/
    }
    cout<< s << endl;
    return 0;
}