#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
ll mod=1e9+7;
ll mod2=998244353;
const int INF=1e9;

signed main(){
	ll n,m;
    cin>>n>>m;
    vector<ll> imos(n+1,0);
    rep(i,m){
        ll l,r;
        cin>>l>>r;
        l--;
        r--;
        imos[l]++;
        imos[r+1]--;
    }
    ll ans=0;
    ll nm=0;
    rep(i,n+1){
        nm+=imos[i];
        if(nm==m)ans++;
    }
    cout<<ans<<endl;
}

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