#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define vi vector<ll>
#define f(i,a,b) for(ll i=a;i<b;i++)
#define fr(i,a,b) for(ll i=a;i>=b;i--)
#define fa(e,l) for(auto e:l)
#define all(arr) arr.begin(),arr.end()
#define pii pair<ll,ll>
#define tii tuple<ll,ll,ll>
#define coutpii(x) fa(e,x){cout<<e.first<<","<<e.second<<" ";}cout<<"\n"
#define coutll(x) fa(e,x){cout<<e<<" ";}cout<<"\n"
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
ll T,a,b,c,d,n,l,r,x,y,m,t,q;
// cin>>T;
// f(I,0,T){
// cin>>n;
// }
cin>>l>>r;
ll mx=0;
f(i,0,r){
cin>>x;
f(i,0,x){
cin>>y;
mx=max(mx,y);
}
}
if(y<l){cout<<0;}
else{cout<<mx*2-l;}
}
