#include <bits/stdc++.h>

using namespace std;

int n,k;

double eps = 1e-9;

int solveLinear(vector<vector<double>>& A, vector<double>& b, vector<double>&x){
		int n= A.size();
		int m = x.size();
		int rank = 0;
		int br, bc;
		if(n) assert(A[0].size() == m);
		vector<int> col(m); iota(col.begin(), col.end(), 0);
		
		for(int i=0; i<n; i++){
				double v, bv = 0;

				for(int r= i; r<n; r++) for(int c = i; c<m; c++)
						if((v=fabs(A[r][c]))>bv)
								br=r, bc=c, bv=v;
				if(bv<=eps){
						for(int j=i; j<n; j++) if(fabs(b[j]) > eps) return -1;
						break;
				}
				
				swap(A[i], A[br]);
				swap(b[i], b[br]);
				swap(col[i], col[bc]);
				for(int j=0; j<n; j++) swap(A[j][i], A[j][bc]);
				bv = 1/A[i][i];
				for(int j = i+1; j<n; j++){
						double fac = A[j][i] * bv;
						b[j]-=fac * b[i];
						for(int k = i+1; k<m; k++) A[j][k] -= fac * A[i][k];
				}
				rank++;
		}

		x.assign(m, 0);

		for(int i=rank; i--;){
				b[i] /= A[i][i];
				x[col[i]] = b[i];
				for(int j=0; j<i; j++) b[j] -=A[j][i] * b[i];
		}

		return rank;
}

bool check(vector<vector<double>> mat, int l, int r){
		vector<double> right(mat.size(), 0);

		for(int i = 0; i<k; i++){
				if(i < l || i > r){
						vector<double> v(k, 0);
						v[i] = 1;
						mat.push_back(v);
						right.push_back(0);
				}
		}

		vector<double> trash(k, 0);



		int s = solveLinear(mat, right, trash);
		bool res = s < trash.size();
		return res;
}

int main(){
		cin>>n>>k;


		// [vertex][type]
		vector<vector<double>> mat(n, vector<double>(k, 0));

		for(int i=0; i<k; i++){
				int n;
				cin >>n;
				for(int j=0; j<n; j++){
						int u,v;
						cin>>u>>v;
						u--;v--;

						mat[u][i]--;
						mat[v][i]++;
				}
		}

		int INF = 100000000;

		int res = INF;
		
		int r = 0;

		for(int l = 0; l<k; l++){
				while(!check(mat,l,r)){
						r++;
						if(r>=k) goto end;
				}
				res = min(res, r-l+1);
		}
end :
		cout << (res == INF?-1 : res) << endl;
}