/**

   Author : sea_26

**/

#pragma GCC optimize("03")
#include <bits/stdc++.h>

using namespace std;

using ull = unsigned long long;
using ll = long long;
using ld = long double;

priority_queue<int> pq;


const int M = 1e9 + 7;
const ll MOD = 998244353;
const ld eps = 1e-9;
const ld PI = acos(-1.0);

// const double pi = atan2(0, -1);
// const double PI = 4 * atan(1);
// const double pi = 2*cos(0.0);

const int iinf = 0x3f3f3f3f;
const ll linf = 0x3f3f3f3f3f3f3f3f;

#define mp make_pair
#define eb emplace_back
#define ep emplace
#define f first
#define s second
#define sz size()

#define bp(n)  __builtin_popcount(n)
#define bclz(n) __builtin_clzll(n)
#define bctz(n) __builtin_ctzll(n)
#define bip(n) __builtin_parity(n)

#define vsort(v) sort(v.begin(),v.end())
#define rvsort(v) sort(v.begin(),v.end(),greater<int>())
#define mnv(v) *min_element(v.begin(),v.end())
#define mxv(v) *max_element(v.begin(),v.end())
#define all(v) (v).begin(),(v).end()
#define ita(v) iota(all(v), 0)

#define ub upper_bound
#define lb lower_bound
#define cr(n) (floor)cbrt(n)
#define msz(a) memset(a, 0, sizeof(a))
#define msm(a) memset(a, 0xff, sizeof(a))

#define rep(n) for(int j=0; j<n; j++)
#define rrep(n) for(int i=n-1; i>=0; i--)
#define lrep(p,q) for(int i=p; i<=q; i++)
#define ldrep(p,q) for(int i=p; i>=q; i--)
#define rsrep(n) for(ll i=1; i*i<=n; i++)
#define it(v)  for(auto p: v)
#define yes cout << "YES" << endl
#define no cout << "NO" << endl

#define fs ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);

template< typename T> inline T MAX(T a, T b){ return a ^ ((a ^ b) & -(a < b)); }
template< typename T> inline T MIN(T a, T b){ return b ^ ((a ^ b) & -(a < b)); }
template< typename T> void tpns(T n){ rrep(30){ if(n & (1 << i)) pq.push(1 << i); } }
template< typename T> void SWAP(T &a, T &b){ a = ((a) ^= (b)),  b = ((b) ^= (a)),  a = ((a) ^= (b)); }
template< typename T> inline T mod(T a, T b){ return a >= b ? a % b : a; }
template< typename T> inline T gcd(T a, T b){ while (b) b ^= a ^= b ^= a %= b; return a; }
///template< typename T> inline T gcd(T a, T b) {while(b){int r = a % b; a = b; b = r;}return a; } /// T.C : log(a+b)
template< typename T> inline T lcm(T a, T b){ return (a / gcd(a,b)) * b; }
template< typename T> T sqr(T x){ return x * x; }
template< typename T> T bigmod(T n,ll p, T M){ if(!p) return 1; else{ T r = sqr(bigmod(n,p >> 1, M))%M; if(p&1) r = (r*n)%M; return r; }}
template< typename T> T exgcd(T a, T b, T& x, T& y){ if(!b){ x = 1; y = 0;return a;} else{T g = exgcd(b,a%b,y,x); y -= (a/b)*x; return g;}}
template< typename T> T icbrt(T mul){T r = cbrt(mul) + 1; while(r * r * r > mul) r--; return r; } /// 54229668

///ll gcdextd(ll a, ll b, ll& x, ll& y) { if (!a) { x = 0; y = 1; return b; }  ll y1,d; d = gcdextd(b % a, a, y, y1);  x = y1 - (b / a) * y; return d; }
ll takemod(ll a){return ((a % M) + M) % M; }
ll fexpo(ll base, ll e){ ll res = 1; while(e > 0){ if(e & 1) res = (res * base) % M; base = (base * base ) % M; e >>= 1; } return 0; }
ll modinv(ll a){return takemod(fexpo(takemod(a), M-2));}

void ReT(){ cout << "\nTime = " << fixed << setprecision(3) << double(clock()) / CLOCKS_PER_SEC  << " Sec"<< endl; exit(0);}


int res, n, m;
const int N = 1e5+10;
int a[N], b[N];
int flag;

int main(){

    fs;
    cin >> n >> m;
    int l = 1, r = n;
    rep(m){
        cin >> a[j] >> b[j];
        l = MAX(l,a[j]);
        r = MIN(r,b[j]);
    }
    cout << MAX(r - l + 1, 0) << endl;
    ///ReT()
return 0;
}


Measured memory_bytes: 1024