#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_M = 1000;
const int INF = 1 << 30;

const int dxs[] = {1, 0, -1, 0};
const int dys[] = {0, 1, 0, -1};

/* typedef */

typedef pair<int,int> pii;
typedef vector<pii> vpii;

struct ISect {
  int i, x, y;
  int nbrs[4], ds[4];
};

struct Stat {
  int d, i, di;
  Stat() {};
  Stat(int _d, int _i, int _di): d(_d), i(_i), di(_di) {};
  bool operator>(const Stat& s0) const { return d > s0.d; }
  void print() { printf("Stat:d=%d, i=%d, di=%d\n", d, i, di); }
};

/* global variables */

int m, n;
ISect isects[MAX_M];
map<string,int> nmhash;
int dists[MAX_M][4], npis[MAX_M][4];

/* subroutines */

/* main */

int main() {
  for (;;) {
    cin >> m >> n;
    if (m == 0) break;

    nmhash.clear();

    for (int i = 0; i < m; i++) {
      string name;
      cin >> name >> isects[i].x >> isects[i].y;
      isects[i].i = i;
      nmhash[name] = i;
      for (int j = 0; j < 4; j++)
	isects[i].nbrs[j] = -1, isects[i].ds[j] = 0;
    }

    for (int i = 0; i < n; i++) {
      string nm0, nm1;
      cin >> nm0 >> nm1;
      ISect* is0 = &isects[nmhash[nm0]];
      ISect* is1 = &isects[nmhash[nm1]];

      int dx = is1->x - is0->x;
      int dy = is1->y - is0->y;

      if (dx != 0) {
	if (dx > 0) {
	  is0->nbrs[0] = is1->i;
	  is1->nbrs[2] = is0->i;
	  is0->ds[0] = is1->ds[2] = dx;
	}
	else {
	  is0->nbrs[2] = is1->i;
	  is1->nbrs[0] = is0->i;
	  is0->ds[2] = is1->ds[0] = -dx;
	}
      }
      else {
	if (dy > 0) {
	  is0->nbrs[1] = is1->i;
	  is1->nbrs[3] = is0->i;
	  is0->ds[1] = is1->ds[3] = dy;
	}
	else {
	  is0->nbrs[3] = is1->i;
	  is1->nbrs[1] = is0->i;
	  is0->ds[3] = is1->ds[1] = -dy;
	}
      }
    }

    string stnm, glnm;
    cin >> stnm >> glnm;

    int st = nmhash[stnm];
    int gl = nmhash[glnm];
    //printf("st=%d, gl=%d\n", st, gl);
    
    priority_queue<Stat,vector<Stat>,greater<Stat> > q;

    for (int di = 0; di < 4; di++) {
      for (int i = 0; i < m; i++) dists[i][di] = INF;
      dists[st][di] = 0;
      npis[st][di] = 1;
      q.push(Stat(0, st, di));
    }

    int min_dist = INF;
    int min_npi = 0;
    
    while (! q.empty()) {
      Stat u = q.top(); q.pop();
      //u.print();
      
      if (u.d != dists[u.i][u.di]) continue;
      if (u.i == gl) {
	if (min_dist > u.d) {
	  min_dist = u.d;
	  min_npi = npis[u.i][u.di];
	}
	else if (min_dist == u.d && min_npi > npis[u.i][u.di])
	  min_npi = npis[u.i][u.di];
	continue;
      }

      ISect& isu = isects[u.i];
      for (int di = 0; di < 2; di++) {
	int vdi = (u.di + di) & 3;
	int vi = isu.nbrs[vdi];
	if (vi >= 0) {
	  int vd = u.d + isu.ds[vdi];
	  int vnpi = npis[u.i][u.di] + 1;
	  if (dists[vi][vdi] > vd) {
	    dists[vi][vdi] = vd;
	    npis[vi][vdi] = vnpi;
	    q.push(Stat(vd, vi, vdi));
	  }
	  else if (dists[vi][vdi] == vd && npis[vi][vdi] > vnpi) {
	    npis[vi][vdi] = vnpi;
	    q.push(Stat(vd, vi, vdi));
	  }
	}
      }
    }

    if (min_dist >= INF)
      cout << "impossible" << endl;
    else
      cout << min_npi << endl;
  }

  return 0;
}

Measured memory_bytes: 1480