#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <string>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <fstream>
#include <cassert>
#include <cstring>
#include <numeric>
#include <ctime>
#include <complex>
#include <bitset>
#include <random>
#include <stack>

using namespace std;

typedef long long ll;
typedef long double ld;

#define int ll
#define double ld
#define loop(i, n) for(int i = 0; i < (int)n; ++i)
#define loop1(i, n) for(int i = 1; i <= (int)n; ++i)
#define F first
#define S second
#define pb push_back
#define pi pair <int, int>
#define all(x) begin(x), end(x)
#define ti tuple <int, int, int>
#define Point Vect
#define mkt make_tuple
#define no {cout << -1; return;}

void solve() {
    int L = 0, R = 1000000;
    int n, m;
    cin >> n >> m;
    loop(i, m) {
        int l, r;
        cin >> l >> r;
        L = max(l, L);
        R = min(R, r);
    }
    if (R < L)
        cout << 0;
    else
        cout << R - L + 1;
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    //int t; cin >> t; loop(i, t)
    solve();
    return 0;
}
#include<iostream>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<cmath>


using namespace std;

#define rep(i,N) for(int i=0;i<N;i++) //0から
#define REP(i,N) for(int j=i;j<N;j++) //iから

typedef long long ll;




ll binary_search(vector<ll> a, ll n, ll key){
    ll right = n, left = -1;
    ll md = (right + left) / 2;

    while(right - left > 1){
        if(a[md] <= key){
            right = md;
        }else{
            left = md;
        }
        md = (right + left) / 2;
    }
    if(left == -1) return -1; //無い場合
    return right;
}

vector<ll> prime;
void Prime(ll n){ //線形篩,素数列挙
    vector<ll> p(n,0);
    p[0]=1;
    p[1]=1;
    for(ll i=2;i<n;i++){
        if(p[i]==0){
            prime.push_back(i);
            p[i]=i;
        }
        ll k=prime.size();
        for(ll j=0;j<k && i*prime[j]<n && prime[j]<=p[i];j++){
            p[i*prime[j]]=prime[j];
        }
    }
}

#define MOD ((ll)1e+9 + 7)




//cout<<fixed<<setprecision(10);
int main(){
    int n,m;
    cin>>n>>m;
    vector<int> L(m),R(m+1);
    rep(i,m){
        cin>>L[i]>>R[i];
        L[i]--;
    }
    vector<int> cnt(n+1,0);
    rep(i,m){
        cnt[L[i]]++;
        cnt[R[i]]--;
    }
    rep(i,n){
        cnt[i+1]+=cnt[i];
    }
    int ans=0;
    rep(i,n){
        if(cnt[i]==m){
            ans++;
        }
    }
    cout<<ans<<endl;

    return 0;
}

