#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define all(c) c.begin(), c.end()
#define endl "\n"
const double PI=3.141592653589;
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define dbg(x...) cerr << "LINE(" << __LINE__ << ") -> " <<"[" << #x << "] = ["; _print(x)
#else
#define dbg(x...)
#endif
void solve()
{
int L,k;
cin >> L >> k;
int mx = 0;
for(int i = 1;i<=k;++i){
int v;
cin >> v;
int sum = 0;
for(int j = 0;j<v;++j){
int x;
cin >> x;
sum+=x;
}
mx = max(mx,sum);
}
int l = max(1ll,L-mx+1), R = mx;
cout << max(0ll,R-l+1) << endl;
}
int32_t main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
int T=1;
for(int i = 1;i<=T;++i)
{
// cout << "Case #" << i << ": ";
solve();
}
}
