#include<bits/stdc++.h>
using namespace std;
#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);
#define ll long long int
#define ull unsigned long long int
#define ld long double
#define mode 1000000007
#define inf 1000000000000000007
#define eps 0.00000001
#define pi 3.141592653589793
#define pii pair<int,int>
#define pdd pair<ld,ld>
#define pll pair<ll,ll>
#define ff first
#define ss second
#define vii vector<int>
#define vpl vector<pll>
#define vll vector<ll>
#define sti stack <int>
#define stll stack <ll>
#define mseti multiset <ll>
#define msetd multiset <ll, greater <ll> >
#define mp make_pair
#define pb push_back
#define lb lower_bound
#define ub upper_bound 
#define stp setprecision(20)//use fixed before stp
#define endl '\n'
int main()
{  
    FAST
    ll n,m;
    cin>>n>>m;
    ll min=0,max=inf;
    ll l,r;
    for(ll i=0;i<m;i++)
    {
        cin>>l>>r;
        if(l>min)
            min=l;
        if(r<max)
            max=r;
    }
    ll ans=max-min+1;
    if(ans<0)
        ans=0;
    cout<<ans;
}