$emmm……$

#include <iostream>
using namespace std;
int main()
{
	int L, M, k1, k2, a[10001] = {}, x = 0;
	cin >> L >> M;
	for (int i = 1; i <= M; i++)
    {
		cin >> k1 >> k2;
		for (int j = k1; j <= k2; j++)
			a[j] = 1;
	}
	for (int i = 0; i <= L; i++)
		if (a[i] == 0)
			x++;
	cout << x << endl;
    return 0;
}

#include <iostream>
using namespace std;
bool tree[10001];
int main (){
    int L,M,sum=0;
    cin>>L>>M;
    int x,y;
    for (int i=0;i<=L;i++){
        tree[i]=1;
    }
    for (int i=0;i<=M;i++){
        cin>>x>>y;
        for (int j=x;j<=y;j++){
            tree[j]=0;
        }
    }
    for (int i=0;i<=L;i++){
        if (tree[i]==1){
            sum++;
        }
    }
    cout << sum <<endl;
    return 0;
}

#include <iostream> using namespace std; bool tree[10001]; int main (){ int L,M,sum=0; cin>>L>>M; int x,y; for (int i=0;i<=L;i++){ tree[i]=1; } for (int i=0;i<=M;i++){ cin>>x>>y; for (int j=x;j<=y;j++){ tree[j]=0; } } for (int i=0;i<=L;i++){ if (tree[i]==1){ sum++; } } cout << sum <<endl; return 0; }