#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> p32;
typedef pair<ll, ll> p64;
typedef pair<double, double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int>> vv32;
typedef vector<vector<ll>> vv64;
typedef vector<vector<p64>> vvp64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
ll MOD = 998244353;
double eps = 1e-12;
#define forn(i, e) for (ll i = 0; i < e; i++)
#define forsn(i, s, e) for (ll i = s; i < e; i++)
#define rforn(i, s) for (ll i = s; i >= 0; i--)
#define rforsn(i, s, e) for (ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout << #x << " = " << x << ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
int main()
{
//ifstream cin("be.txt");
/*
int n; cin>>n;
vector<int> a(n+1);
multiset<int> s;
for(int i=1; i<=n; i++){
cin>>a[i];
s.insert(a[i]);
}
for(int i=1; i<=n; i++){
s.erase(s.lower_bound(a[i]));
if(!s.count(a[i])){
cout<<i;
break;
}
}*/
// aruszallitas ures szakaszai
int n;
cin >> n;
vector<int> a(n + 1);
int m;
cin >> m;
while (m)
{
int k, v;
cin >> k >> v;
a[k]++;
a[v]--;
m--;
}
int ans = 0;
for (int i = 2; i < n; i++)
{
a[i] += a[i - 1];
if (a[i - 1] != 0 && a[i] == 0)
ans++;
}
if (a[1] == 0)
ans++;
cout << ans;
return 0;
}