#include <stdio.h>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <unordered_set>
#include <queue>
#include <stack>
#include <functional>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <limits>

using namespace std;

#define ll long long

#define in(x) cin >> x
#define out(x) cout << x << endl

#define PI acos(-1)
#define pp push_back

#define Yes cout << "Yes" << endl
#define YES cout << "YES" << endl
#define No cout << "No" << endl
#define NO cout << "NO" << endl

#define vec2(type) vector<vector<type>>
#define vec3(type) vector<vector<vector<type>>>

#define For(i, n) for(int i = 0; i < n; i++)

#define inRange(x, a, b) (a <= x && x <= b)
#define between(x, a, b) (a < x && x < b)

template<typename T> void swap(T &a, T &b){
	T temp = a;
	a = b;
	b = temp;
}

template<typename T> void input(T *data, int n){
	For(i, n){
		cin >> data[i];
	}
}

template<typename T> void input(vector<T> &vec, int n){
	T temp;
	For(i, n){
		cin >> temp;
		vec.push_back(temp);
	}
}

template<typename T> void sort(vector<T> &ary){
	sort(ary.begin(), ary.end());
}

template<typename T> void rsort(vector<T> &ary){
	sort(ary.rbegin(), ary.rend());
}

void rstring(string &str){
	string temp = str;

	For(i, (int)str.size()){
		str[i] = temp[(str.size() - 1) - i];
	}
}

struct Vec{
	int x, y;
	Vec():
	x(0), y(0){}
	Vec(int _x, int _y):
	x(_x), y(_y){}
};

template<typename T> void print(T *x, int n){
	For(i, n){
		cout << x[i] << " ";
	}
	cout << endl;
}

template<typename T> void print(vector<T> &x){
	For(i, (int)x.size()){
		cout << x[i] << " ";
	}
	cout << endl;
}

template<typename T>
T gcd(T n, T m){
	if(n % m == 0){
		return m;
	}
	else{
		return gcd<T>(m, n % m);
	}
}

template<typename T> T binarySearch(vector<T> a, T target){
	int cur = (int)a.size() / 2;
	int upper = (int)a.size() - 1;
	int buttom = 0;
	while(1){
		if(a[cur] == target){
			return a[cur];
		}
		else if(a[cur] > target){
			upper = cur;
			cur = (buttom + cur) / 2;
		}
		else{
			buttom = cur;
			cur = (cur + upper) / 2;
		}
	}
}

template<typename T> T binarySearch(vector<T> a, T func(T), T target){
	int cur = (int)a.size() / 2;
	int upper = (int)a.size() - 1;
	int buttom = 0;
	while(1){
		int value = func(a[cur]);
		if(value == target){
			return a[cur];
		}
		else if(value > target){
			upper = cur;
			cur = (buttom + cur) / 2;
		}
		else{
			buttom = cur;
			cur = (cur + upper) / 2;
		}
	}
}

struct UnionFind {
    vector<int> par; // par[i]:iの親の番号　(例) par[3] = 2 : 3の親が2

    UnionFind(int N) : par(N) { //最初は全てが根であるとして初期化
        for(int i = 0; i < N; i++) par[i] = i;
    }
	UnionFind(){}

    int root(int x) { // データxが属する木の根を再帰で得る：root(x) = {xの木の根}
        if (par[x] == x) return x;
        return par[x] = root(par[x]);
    }

    void unite(int x, int y) { // xとyの木を併合
        int rx = root(x); //xの根をrx
        int ry = root(y); //yの根をry
        if (rx == ry) return; //xとyの根が同じ(=同じ木にある)時はそのまま
        par[rx] = ry; //xとyの根が同じでない(=同じ木にない)時：xの根rxをyの根ryにつける
    }

    bool same(int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す
        int rx = root(x);
        int ry = root(y);
        return rx == ry;
    }

    int size(){
    	int count = 0;
    	for (int i = 0; i < (int)par.size(); i++){
    		if (par[i] == i){
    			count++;
    		}
    	}
    	return count;
    }
};

int main(){

	int n, m;
	int  l, r;


	cin >> n >> m;
	cin >> l >> r;

	int max_ = r, min_ = l;
	For(i, n - 1){
		cin >> l >> r;
		max_ = min(max_, r);
		min_ = max(min_, l);
	}

	out(max(max_ - min_ + 1, 0));
	
	return 0;

}

Measured memory_bytes: 256