#include<iostream>
#include<stdio.h>
#include<vector>
#include<cmath>
#include<algorithm>
#include<map>
#include<cstdlib>
#include<cstring>
#include <exception>

using namespace std;

struct Edge{
    int tBegin;
    int tEnd;
    int dst;
};

int main(){ freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    int n, end, m;
    cin>>n>>end>>m;
    vector<vector<Edge> > out(1 + n);
    for(int i = 0; i < m; i++){
        int len;
        cin>>len;
        int prevSt,prevT;
        cin>>prevSt>>prevT;
        for(int j = 1; j < len; j++){
            int curSt,curT;
            cin>>curSt>>curT;
            out[prevSt].push_back(Edge{prevT, curT, curSt});
            prevSt = curSt;
            prevT = curT;
        }
    }
    const int INF = 1e9 + 1;
    vector<int> d(1 + n,INF);
    d[1] = 0;
    vector<bool> u(1 + n, 0);
    while(true){
        int v = -1;
        for(int i = 1; i <= n; i++){
            if(!u[i] && (v==-1 || d[i] < d[v])){
                v = i;
            }
        }
        if(v == -1 || d[v]== INF)
            break;
        u[v] = 1;
        for(const Edge &edge : out[v]){
            if(edge.tBegin >= d[v]){
                if(edge.tEnd < d[edge.dst]){
                    d[edge.dst] = edge.tEnd;
                }
            }
        }
    }
    if(d[end] == INF){
        cout<<-1;
    }
    else{
        cout<<d[end];
    }
    return 0;
}