#include <bits/stdc++.h>

using namespace std;

//typedefs

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef pair<int,int> PII;
typedef pair<double, double> PDD;
typedef pair<LL, LL> PLL;
typedef vector<PII> VII;
typedef vector<PLL> VLL;

//#Defines
#define rep(i,a,b)	for(i=a;i<=b;i++)
#define repR(i,a,b)	for(i=a;i>=b;i--)
#define pb push_back
// #define pb emplace_back
#define F first
#define S second
#define mp make_pair
#define all(c)		c.begin(),c.end()
#define endl '\n'
#define pf printf
#define sf scanf
#define MOD 1000000007
//#define harmonic(n) 0.57721566490153286l+log(n)
//if harmonic numbers need to be calculated, precalculate upto 1e6, then for any x > 1e6
//call harmonic(x + 0.5)
#define RESET(a,b)	memset(a,b,sizeof(a))
#define sqr(a) ((a) * (a))

#define optimize() ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

const double PI = acos(-1);
const double eps = 1e-9;
const int inf = 2000000000;
const LL infLL = 9000000000000000000;


//Bit Operations
inline bool checkBit(LL n, int i) { return n&(1LL<<i); }
inline LL setBit(LL n, int i) { return n|(1LL<<i);; }
inline LL resetBit(LL n, int i) { return n&(~(1LL<<i)); }

//Rotation: S -> E -> N -> W
int fx[] = {0, +1, 0, -1};
int fy[] = {-1, 0, +1, 0}; 
//int dx[] = {0, +1, +1, +1, 0, -1, -1, -1};
//int dy[] = {-1, -1, 0, +1, +1, +1, 0, -1};

//Inline functions

inline bool EQ(double a, double b) { return fabs(a-b) < 1e-9; }
inline bool isLeapYear(LL year) { return (year%400==0) || (year%4==0 && year%100!=0); }
inline void normal(LL &a) { a %= MOD; (a < 0) && (a += MOD); }
inline LL modMul(LL a, LL b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a*b)%MOD; }
inline LL modAdd(LL a, LL b) { a %= MOD, b %= MOD; normal(a), normal(b); return (a+b)%MOD; }
inline LL modSub(LL a, LL b) { a %= MOD, b %= MOD; normal(a), normal(b); a -= b; normal(a); return a; }
inline LL modPow(LL b, LL p) { LL r = 1; while(p) { if(p&1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }
inline LL modInverse(LL a) { return modPow(a, MOD-2); }
inline LL modDiv(LL a, LL b) { return modMul(a, modInverse(b)); }
inline bool isInside(PII p,LL n,LL m)	{ return (p.first>=0&&p.first<n&&p.second>=0&&p.second<m); }
inline bool isInside(PII p,LL n)		{ return (p.first>=0&&p.first<n&&p.second>=0&&p.second<n); }
inline bool isSquare(LL x) 				{ LL s = sqrt(x);	return (s*s==x); }
inline bool isFib(LL x) 				{ return isSquare(5*x*x+4)|| isSquare(5*x*x-4); }
inline bool isPowerOfTwo(LL x)			{ return ((1LL<<(LL)log2(x))==x); }
inline LL gcd(LL a, LL b) {return __gcd(a, b);}
inline LL lcm(LL a, LL b) {return (a * (b / gcd(a, b))); }

//Prime Number Generator
/*
#define mx 1000006
bitset <mx> mark;
vector <int> primes;

void sieve() {
    mark[0] = mark[1] = 1;
    primes.push_back(2);
    int lim = sqrt(mx * 1.0) + 2;
    for (int i = 4; i < mx; i += 2) mark[i] = 1;
    for (int i = 3; i < mx; i += 2) {
        if (!mark[i]) {
            primes.push_back(i);
            if (i <= lim)
                for (int j = i * i; j < mx; j += i)
                    mark[j] = 1;
        }
    }
}
*/

int main() {
    // #ifndef ONLINE_JUDGE
    //     freopen("in", "r", stdin);
    //     freopen("out", "w", stdout);
    // #endif
    optimize();
    int n, m; cin >> n >> m;
    int ans = 0;
    int l = 1, r = n;
    for (int i = 0; i < m; i++) {
        int lx, rx; cin >> lx >> rx;
        l = max(l, lx);
        r = min(r, rx);
    }

    if (l > r) {
        cout << 0 << endl;
    } else {
        cout << r - l + 1 << endl;
    }
}

Measured memory_bytes: 256