#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_set>
#include <queue>

using namespace std;

#define INF (1e18)

typedef pair<long long,long long> P;
typedef pair<long long,P> P2;

int main() {
    int M,N,K;
    cin >> M >> N >> K;

    vector<P2> sw;
    sw.push_back(P2(0,P(1,1)));

    for(int i=1; i<=K; ++i) {
        long long a,b;
        cin >> a >> b;
        sw.push_back(P2(i,P(a,b)));
    }

    sw.push_back(P2(K+1,P(M,N)));

    vector<vector<P> > to[2];
    to[0].resize(K+2);
    to[1].resize(K+2);

    sort(sw.begin(),sw.end(), [](P2& lhs, P2& rhs) {
        return (lhs.second.first==rhs.second.first)?
            ((lhs.second.second==rhs.second.second)?
                (lhs.first<rhs.first):(lhs.second.second<rhs.second.second))
            :(lhs.second.first<rhs.second.first);
    });

    for(int i=1; i<=K+1; ++i) {
        if(sw[i-1].second.first==sw[i].second.first) {
            long long d=sw[i].second.second-sw[i-1].second.second;
            to[0][sw[i-1].first].push_back(P(sw[i].first,d));
            if(sw[i-1].first!=0) to[0][sw[i].first].push_back(P(sw[i-1].first,d));
        }
    }

    sort(sw.begin(),sw.end(), [](P2& lhs, P2& rhs) {
        return (lhs.second.second==rhs.second.second)?
            ((lhs.second.first==rhs.second.first)?
                (lhs.first<rhs.first):(lhs.second.first<rhs.second.first))
            :(lhs.second.second<rhs.second.second);
    });

    for(int i=1; i<=K+1; ++i) {
        if(sw[i-1].second.second==sw[i].second.second) {
            long long d=sw[i].second.first-sw[i-1].second.first;
            to[1][sw[i-1].first].push_back(P(sw[i].first,d));
            if(sw[i-1].first!=0) to[1][sw[i].first].push_back(P(sw[i-1].first,d));
        }
    }

    sort(sw.begin(),sw.end());

    priority_queue<P2,vector<P2>,greater<P2> > q;
    vector<long long> dist[2];
    dist[0].resize(K+2,INF);
    dist[1].resize(K+2,INF);
    unordered_set<long long> visited[2];
    q.push(P2(0,P(0,0))); // dist, from, sw
    dist[0][0]=0;
    visited[1].insert(0);
    while(!q.empty()) {
        P2 pp=q.top(); q.pop();
        long long now_dist=pp.first;
        long long now_from=pp.second.first;
        long long now_sw=pp.second.second;
        if(sw[now_sw].second.first==M && sw[now_sw].second.second==N) {
            dist[now_from][K+1]=now_dist;
            break;
        }
        if(visited[now_from].count(now_sw)!=0 || dist[now_from][now_sw]<now_dist) continue;
        visited[now_from].insert(now_sw);

        for(int i=0; i<(int)to[now_from][now_sw].size(); ++i) {
            long long nxt_sw=to[now_from][now_sw][i].first;
            long long nxt_dist=to[now_from][now_sw][i].second+now_dist;
            if(visited[now_from].count(nxt_sw)!=0 || dist[now_from][nxt_sw]<=nxt_dist) continue;
            dist[now_from][nxt_sw]=nxt_dist;
            q.push(P2(nxt_dist,P(now_from,nxt_sw)));
        }
        if(now_sw!=0) {
            for(int i=0; i<(int)to[(now_from+1)%2][now_sw].size(); ++i) {
                long long nxt_sw=to[(now_from+1)%2][now_sw][i].first;
                long long nxt_dist=to[(now_from+1)%2][now_sw][i].second+now_dist+1;
                if(visited[(now_from+1)%2].count(nxt_sw)!=0 || dist[(now_from+1)%2][nxt_sw]<=nxt_dist) continue;
                dist[(now_from+1)%2][nxt_sw]=nxt_dist;
                q.push(P2(nxt_dist,P((now_from+1)%2,nxt_sw)));
            }
        }
    }

    long long ans=min(dist[0][K+1],dist[1][K+1]);
    if(ans==INF) ans=-1;

    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 55188