#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 fst first
#define scd second
#define PB push_back
#define MP make_pair
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define omajinai ios::sync_with_stdio(false);cin.tie(0)
#define rep(i,x) for(int i=0;i<(int)(x);++i)
#define rep1(i,x) for(int i=1;i<=(int)(x);++i)

using ll=long long;
using ld=long double;
using vi=vector<int>;
using vvi=vector<vi>;
using pii=pair<int, int>;
using vpii=vector<pii>;

template<class T,class U>ostream&operator<<(ostream&os,const pair<T,U>p){os<<"("<<p.fst<<", "<<p.scd<<")";return os;}
template<class T>ostream&operator<<(ostream&os,const vector<T>v){rep(i,v.size()){if(i)os<<", ";os<<v[i];}return os;}
template<typename T>T&max(T&a,T&b){if(a>=b)return a;return b;}
template<typename T>T&min(T&a,T&b){if(a < b)return a;return b;}
template<typename T>bool chmax(T&a,T b){if(a < b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a > b){a=b;return true;}return false;}
int in(){int a;scanf("%d",&a);return a;}
ll lin(){ll a;scanf("%lld",&a);return a;}

constexpr int inf = 1e9;
constexpr ll linf = 3e18;
constexpr double eps = 1e-9;

typedef pii Pos;
typedef pair<Pos, bool> State; // ??§?¨?, ????????????????????????
typedef pair<int, State> Data;

int M, N, K;

vi row[100010];
vi col[100010];
map<State, int> d;
priority_queue<Data, vector<Data>, greater<Data> > q;

void queue_init()
{
    int x=0;
    if (row[x].empty()) return;
    int yidx = lower_bound(all(row[x]), 0) - begin(row[x]);

    q.push(Data(row[x][yidx], State(Pos(row[x][yidx], 0), true)));
    if (yidx == 0) {
        q.push(Data(1, State(Pos(0, 0), false)));
    }
}

signed main()
{
    M = lin(), N = lin(), K = lin();

    rep(i, K) {
        int x = lin() - 1, y = lin() - 1;

        row[x].PB(y);
        col[y].PB(x);
    }

    row[M - 1].PB(N - 1);
    col[N - 1].PB(M - 1);

    rep(i, 100010) sort(all(row[i])), sort(all(col[i]));

    Pos start = Pos(0, 0);
    Pos goal = Pos(N - 1, M - 1);

    d[State(start, true)] = 0;

    queue_init();

    while (q.size()) {
        Data dat = q.top(); q.pop();

        State state = dat.scd;
        Pos p = state.fst;
        int y = p.fst, x = p.scd;
        bool is_vertical = state.scd;
        int dist = dat.fst;

        if (d.find(state) != d.end() && d[state] < dist) continue;

        int yidx = lower_bound(all(row[x]), y) - begin(row[x]);
        int xidx = lower_bound(all(col[y]), x) - begin(col[y]);

        if (yidx - 1 >= 0) {
            int nxdist = dist + abs(y - row[x][yidx - 1]) + (is_vertical ? 0 : 1);
            Pos nxpos = Pos(row[x][yidx - 1], x);
            State nxstate = State(nxpos, true);

            if (d.find(nxstate) == d.end() || d[nxstate] > nxdist) {
                d[nxstate] = nxdist;

                q.push(Data(nxdist, nxstate));
            }
        }

        if (yidx + 1 < row[x].size()) {
            int nxdist = dist + abs(y - row[x][yidx + 1]) + (is_vertical ? 0 : 1);
            Pos nxpos = Pos(row[x][yidx + 1], x);
            State nxstate = State(nxpos, true);

            if (d.find(nxstate) == d.end() || d[nxstate] > nxdist) {
                d[nxstate] = nxdist;

                q.push(Data(nxdist, nxstate));
            }
        }

        if (xidx - 1 >= 0) {
            int nxdist = dist + abs(x - col[y][xidx - 1]) + (is_vertical ? 1 : 0);
            Pos nxpos = Pos(y, col[y][xidx - 1]);
            State nxstate = State(nxpos, false);

            if (d.find(nxstate) == d.end() || d[nxstate] > nxdist) {
                d[nxstate] = nxdist;

                q.push(Data(nxdist, nxstate));
            }
        }

        if (xidx + 1 < col[y].size()) {
            int nxdist = dist + abs(x - col[y][xidx + 1]) + (is_vertical ? 1 : 0);
            Pos nxpos = Pos(y, col[y][xidx + 1]);
            State nxstate = State(nxpos, false);

            if (d.find(nxstate) == d.end() || d[nxstate] > nxdist) {
                d[nxstate] = nxdist;

                q.push(Data(nxdist, nxstate));
            }
        }
    }

    int ans = linf;

    if (d.find(State(goal, true)) != d.end()) chmin(ans, d[State(goal, true)]);
    if (d.find(State(goal, false)) != d.end()) chmin(ans, d[State(goal, false)]);

    printf("%lld\n", ans == linf ? -1 : ans);
}

Measured memory_bytes: 46688