#include <iostream>
#include<algorithm>
#include<stdio.h>
#include<vector>
#include<cmath>
#include<cstring>
using namespace std;
int main (){
    
    
    int n,m;
    cin>>n>>m;
    int niz[n+1];
    int nizo[n+1];
    for(int i=0;i<n;i++)
    {
            cin>>niz[i]>>nizo[i];
            }
            if(nizo[0]>niz[0])
            cout<<nizo[0]-niz[0]<<endl;
            else
            cout<<niz[0]-nizo[0]<<endl;


//system("pause");
return 0;
}