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#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstring>
#define maxn 100010
using namespace std;

typedef struct Node{
   
    char c;
    int next;
 //   int flag; 
}N;

N node[maxn];

int main() {
    int first1,first2,N;
    while(cin>>first1>>first2>>N)
    {
        for(int i=0;i<N;i++)
        {
            int add;
            cin>>add;
            cin>>node[add].c>>node[add].next;
        }
        int p1 = first1,l1=0;
        int p2 = first2,l2=0;
        int ans = -1;
        while(p1!=-1)
        {
            l1++;
            p1 = node[p1].next;
        }
        while(p2!=-1)
        {
            l2++;
            p2 = node[p2].next;
        }
        p1 = first1;
        while(l1>l2)
        {
            l1--;
            p1 = node[p1].next;
        }
        p2 = first2;
        while(l1<l2)
        {
            l2--;
            p2 = node[p2].next;
        }
        while(p1!=-1)
        {
            if(p1==p2)
            {
                ans = p1;
                break;
            }
            else {
                p1 = node[p1].next;
                p2 = node[p2].next;
            }
        }
        cout<<ans<<endl;


    }
    
    
}
// 64 位输出请用 printf("%lld")