#include<bits/stdc++.h>

using namespace std;

typedef long long int64;
const int64 INF = 1LL << 58;

struct StronglyConnectedComponents
{
  vector< vector< int > > gg, rg;
  vector< pair< int, int > > edges;
  vector< int > comp, order, used;

  StronglyConnectedComponents(size_t v) : gg(v), rg(v), comp(v, -1), used(v, 0) {}

  void add_edge(int x, int y)
  {
    gg[x].push_back(y);
    rg[y].push_back(x);
    edges.emplace_back(x, y);
  }

  int operator[](int k)
  {
    return (comp[k]);
  }

  void dfs(int idx)
  {
    if(used[idx]) return;
    used[idx] = true;
    for(int to : gg[idx]) dfs(to);
    order.push_back(idx);
  }

  void rdfs(int idx, int cnt)
  {
    if(comp[idx] != -1) return;
    comp[idx] = cnt;
    for(int to : rg[idx]) rdfs(to, cnt);
  }

  void build(vector< vector< int > > &t)
  {
    for(int i = 0; i < gg.size(); i++) dfs(i);
    reverse(begin(order), end(order));
    int ptr = 0;
    for(int i : order) rdfs(i, ptr), ptr++;

    t.resize(ptr);
    set< pair< int, int > > connect;
    for(auto &e : edges) {
      int x = comp[e.first], y = comp[e.second];
      if(x == y) continue;
      if(connect.count({x, y})) continue;
      t[x].push_back(y);
      connect.emplace(x, y);
    }
  }
};

int H, W, N;
int link[500][500];
bool mine[500][500];
int linked[250000];
int64 lazy[250000];

int main()
{
  cin >> H >> W >> N;

  StronglyConnectedComponents scc(H * W);

  for(int i = 0; i < H; i++) {
    for(int j = 0; j < W; j++) {
      int y, x;
      cin >> y >> x;
      link[i][j] = y * W + x;
      linked[i * W + j] = link[i][j];
      if(y == i && x == j) {
        mine[i][j] = true;
      } else {
        scc.add_edge(i * W + j, link[i][j]);
      }
    }
  }

  vector< vector< int > > g;
  scc.build(g);
  vector< vector< int > > ventex(g.size());
  vector< set< int > > query(g.size());
  vector< int > beet(g.size(), 0);
  vector< int > dinamic(H * W, -1);

  for(int i = 0; i < H * W; i++) {
    ventex[scc[i]].push_back(i);
  }
  for(int i = 0; i < g.size(); i++) {
    if(ventex[i].empty()) continue;
    if(ventex[i].size() == 1 && !mine[ventex[i][0] / W][ventex[i][0] % W]) continue;
    beet[i] = true;
  }

  for(int i = 0; i < g.size(); i++) {
    if(ventex[i].empty()) continue;
    if(beet[i]) {
      int now = ventex[i][0];
      int ptr = 0;
      while(dinamic[now] == -1) {
        dinamic[now] = ptr++;
        now = linked[now];
      }
    }
  }

  vector< priority_queue< pair< int, int >, vector< pair< int, int > >, greater< pair< int, int > > > > que(g.size());

  for(int i = 0; i < N; i++) {
    int y, x;
    cin >> y >> x;
    y = y * W + x;

    if(beet[scc[y]]) {
      que[scc[y]].emplace(0, dinamic[y]);
    } else {
      query[scc[y]].emplace(beet[scc[y]] ? dinamic[y] : 0);
    }
  }


  int64 res = INF;
  for(int i = 0; i < g.size(); i++) {

    if(ventex[i].empty()) continue;
    if(!beet[i]) {
      int future = linked[ventex[i][0]];
      bool commit = beet[scc[future]];

      if(commit || query[i].size() < query[scc[future]].size()) {
        for(int j : query[i]) {
          int64 nxt = j + 1 + lazy[i] - lazy[scc[future]];
          if(commit) {
            que[scc[future]].emplace(nxt, dinamic[future] + lazy[scc[future]]);
            continue;
          }
          if(query[scc[future]].count(nxt)) {
            res = min(res, nxt + lazy[scc[future]]);
          } else {
            query[scc[future]].insert(nxt);
          }
        }
      } else {
        lazy[i]++;
        for(int j : query[scc[future]]) {
          int64 nxt = j - lazy[i] + lazy[scc[future]];
          if(query[i].count(nxt)) {
            res = min(res, nxt + lazy[i]);
          } else {
            query[i].insert(nxt);
          }
        }
        swap(lazy[i], lazy[scc[future]]);
        swap(query[i], query[scc[future]]);
      }
    }
  }

  for(int i = 0; i < g.size(); i++) {
    if(ventex[i].empty()) continue;
    if(beet[i]) {
      vector< int > ss(ventex[i].size(), 0);
      while(!que[i].empty()) {
        auto s = que[i].top();
        que[i].pop();
        int nxt = (s.first - s.second + ventex[i].size()) % ventex[i].size();
        if(query[i].count(nxt)) {
          res = min(res, (int64) s.first);
        } else {
          query[i].insert(nxt);
        }

      }
    }
  }


  if(res == INF) {
    cout << -1 << endl;
  } else {
    cout << res << endl;
  }
}

Measured memory_bytes: 110700