#include <iostream>
#include <vector>

using namespace std;

struct att
    {int time; bool able;};

struct rebro
    {int xn;int xk;int yn;int yk;};

int main()
{
    int ns, t, nr;
    cin>>ns>>t>>nr;

    att **rasp=new att*[ns];
    for (int i=0;i<ns;i++)
        rasp[i]=new att[nr];

    for (int i=0;i<ns;i++)
        for (int j=0;j<nr;j++)
        {
            rasp[i][j].time=-1;
            rasp[i][j].able=false;
        }

    for (int i=0;i<nr;i++)
    {
            int nost;
            cin>>nost;
            for (int j=0;j<nost;j++)
            {
                int tost,ttime;
                cin>>tost;
                cin>>ttime;
                rasp[tost-1][i].time=ttime;
            }
    }

    for (int i=0;i<nr;i++)
        rasp[0][i].able=true;

    vector <rebro> graph;

        for (int i=0;i<nr;i++)
            for (int j=0;j<ns;j++)
                for (int k=0;k<ns;k++)
                {
                    if (j!=k && rasp[j][i].time!=-1 && rasp[k][i].time!=-1)
                        if (rasp[j][i].time<=rasp[k][i].time)
                            {
                                rebro reb;
                                reb.yn=i;reb.yk=i;
                                reb.xn=j;reb.xk=k;
                                graph.push_back(reb);
                            }
                }

        for (int i=0;i<ns;i++)
            for (int j=0;j<nr;j++)
                for (int k=0;k<nr;k++)
                {
                    if (j!=k && rasp[i][j].time!=-1 && rasp[i][k].time!=-1)
                        if (rasp[i][j].time<=rasp[i][k].time)
                            {
                                rebro reb;
                                reb.yn=j; reb.yk=k;
                                reb.xn=i; reb.xk=i;
                                graph.push_back(reb);
                            }
                }

        bool flag=false;
        for (int iter=0; iter<ns*nr; iter++)
        {
            flag=false;
            for (int i=0;i<graph.size();i++)
                if (rasp[graph[i].xn][graph[i].yn].able && !rasp[graph[i].xk][graph[i].yk].able)
                {
                    rasp[graph[i].xk][graph[i].yk].able=true;
                    flag=true;
                }
            if (!flag) break;
        }

    int mintime = 1000000001;
    for (int i=0;i<nr;i++)
    {
        if (rasp[t-1][i].able==true && rasp[t-1][i].time<mintime)
            mintime=rasp[t-1][i].time;
    }

    if (mintime==1000000001) cout<<-1;
    else cout<<mintime;

    return 0;
}