#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <functional>
 
using namespace std;
 
#define int long long
#define MP make_pair
#define PB push_back
#define FI first
#define SE second
#define MAX_K 200000
typedef pair<int, pair<int, int> > PPII;
typedef pair<int, int> PII;
static const int INF = 1ll<<60;
static const int dx[] = { 1, -1, 0, 0, };
static const int dy[] = { 0, 0, 1, -1 };
 
int M, N, K;
vector<PII> fld,X,Y;
int D[MAX_K + 5];
bool flg=false;
 
void dijkstra(){
    priority_queue<PPII, vector<PPII>, greater<PPII> > que;
    fill(D, D + MAX_K + 5, INF);
    D[0] = 0;
    que.push(PPII(0, PII(0, 0)));
    while (!que.empty()){
        PPII p = que.top();
        que.pop();
        int v = p.SE.FI;
        int On=p.SE.SE;
        if (D[v]<p.FI)continue;
        int p1=lower_bound(X.begin(),X.end(),PII(fld[v].FI,fld[v].SE))-X.begin();
        int p2=lower_bound(Y.begin(),Y.end(),PII(fld[v].SE,fld[v].FI))-Y.begin();
        for (int i = p1-1; i<=p1+1; i++){
            if(p1==X.size())break;
            if(i<0||i>=X.size())continue;
            int t=lower_bound(fld.begin(),fld.end(),PII(X[i].FI,X[i].SE))-fld.begin();
            PII e = fld[t];
            if (fld[v].FI != e.FI)continue;
            if((!flg)&&e.FI==1&&e.SE==1)continue;
            if(fld[v].FI != e.FI&&fld[v].SE != e.SE)continue;
            int cost = abs(e.FI - fld[v].FI) + abs(e.SE - fld[v].SE);
            if(On==1)cost++;
            if (D[t]>D[v] + cost){
                D[t] = D[v] + cost;
                que.push(PPII(D[t], MP(t, 0)));
            }
        }
        for (int i = p2-1; i<=p2+1; i++){
            if(flg==false&&fld[v].FI==1&&fld[v].SE==1)break;
            if(p2==Y.size())break;
            if(i<0||i>=Y.size())continue;
            int t=lower_bound(fld.begin(),fld.end(),PII(Y[i].SE,Y[i].FI))-fld.begin();
            PII e = fld[t];
            if (fld[v].SE != e.SE)continue;
            if((!flg)&&e.FI==1&&e.SE==1)continue;
            if(fld[v].FI != e.FI&&fld[v].SE != e.SE)continue;
            int cost = abs(e.FI - fld[v].FI) + abs(e.SE - fld[v].SE);
            if(On==0)cost++;
            if (D[t]>D[v] + cost){
                D[t] = D[v] + cost;
                que.push(PPII(D[t], MP(t, 1)));
            }
        }
    }
}
 
signed main(){
    cin >> M >> N >> K;
    fld.PB(PII(1, 1));
    fld.PB(PII(M, N));
    X.PB(PII(1, 1));
    Y.PB(PII(1, 1));
    X.PB(PII(M, N));
    Y.PB(PII(N, M));
    for (int i = 0; i < K; ++i){
        int x, y;
        cin >> x >> y;
        if(x==1&&y==1){
            flg=true;
            continue;
        }
        if(x==M&&y==N)continue;
        fld.PB(PII(x, y));
        X.PB(PII(x, y));
        Y.PB(PII(y, x));
    }
    sort(fld.begin(),fld.end());
    sort(X.begin(),X.end());
    sort(Y.begin(),Y.end());
    dijkstra();
    int ans=lower_bound(fld.begin(),fld.end(),MP(M,N))-fld.begin();
    if (D[ans] >= INF)cout << -1 << endl;
    else cout << D[ans] << endl;
    return 0;
}

Measured memory_bytes: 16448