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#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using PII = pair<int, int>;
template <typename T> using V = vector<T>;
template <typename T> using VV = vector<V<T>>;
template <typename T> using VVV = vector<VV<T>>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll INF = (1LL<<60);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }
template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')';
  return out;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'[';
  REP(i, a.size()) {out<<a[i];if(i!=a.size()-1)out<<',';}
  out<<']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void)
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  int w, h, n;
  cin >> w >> h >> n;
  V<int> x(n), y(n);
  VV<PII> vx(w), vy(h);
  REP(i, n) {
    cin >> x[i] >> y[i], x[i]--, y[i]--;
    vx[x[i]].PB({y[i], i});
    vy[y[i]].PB({x[i], i});
  }

  VV<PII> g(2*n);
  REP(i, w) {
    sort(ALL(vx[i]));
    FOR(j, 1, vx[i].size()) {
      int tx = vx[i][j].second, ty = vx[i][j-1].second;
      int cost = vx[i][j].first - vx[i][j-1].first;
      g[tx].PB({ty, cost});
      g[ty].PB({tx, cost});
    }
  }
  REP(i, h) {
    sort(ALL(vy[i]));
    FOR(j, 1, vy[i].size()) {
      int tx = vy[i][j].second+n, ty = vy[i][j-1].second+n;
      int cost = vy[i][j].first - vy[i][j-1].first;
      g[tx].PB({ty, cost});
      g[ty].PB({tx, cost});
    }
  }
  REP(i, n) {
    g[i].PB({i+n, 1});
    g[i+n].PB({i, 1});
  }

  V<int> d(2*n, INF);
  priority_queue<PII, V<PII>, greater<PII>> que;
  for(auto i: vx[0]) {
    d[i.second] = i.first;
    que.push({d[i.second], i.second});
  }

  while(que.size()) {
    PII t = que.top(); que.pop();
    if(d[t.second] < t.first) continue;
    for(auto i: g[t.second]) {
      if(d[i.first] > d[t.second] + i.second) {
        d[i.first] = d[t.second] + i.second;
        que.push({d[i.first], i.first});
      }
    }
  }

  int ret = INF;
  for(auto i: vx[w-1]) chmin(ret, d[i.second] + h-1 - i.first);
  for(auto i: vy[h-1]) chmin(ret, d[i.second+n] + w-1 - i.first);
  
  if(ret == INF) cout << -1 << endl;
  else cout << ret << endl;

  return 0;
}