#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT_ON(bit, i) (((bit >> i) & 1) > 0)
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;
template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T,typename... Ts> auto make_v(size_t a, Ts... ts){ return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}    // C++14
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename std::enable_if<std::is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline void print_vec(const std::vector<T> &v) { for (int i = 0; i < v.size(); ++i) {  if (i != 0) {std::cout << " ";} std::cout << v[i];} std::cout << "\n"; }
inline bool inside(long long y, long long x, long long H, long long W) {return 0 <= y and y < H and 0 <= x and x < W; }
template<class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }
template<class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) { return abs(x1 - x2) + abs(y1 - y2); }
template<typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template<class T> inline std::vector<T> unique(std::vector<T> v) {
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v;
}
// 初項s, 交差dのn個の数列の和
long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
    return n * (2 * s + (n - 1) * d) / 2;
}

// 2のべき乗数かどうか
bool is_power_of_two(long long x) {
    return !(x & (x - 1));
}

// aとbの最大公約数 O(log min(a, b))
long long gcd(long long a, long long b) {
    if (b == 0) { return a; }
    return gcd(b, a % b);
}

// 数列vの最大公約数 O(N log d)
long long gcd(std::vector<long long> &v) {
    long long ans = v[0];
    for (int i = 1; i < (int)v.size(); ++i) {
        ans = gcd(ans, v[i]);
    }
    return ans;
}

// aとbの最小公倍数 O(log min(a, b))
long long lcm(long long a, long long b) {
    long long g = gcd(a, b);
    return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 60u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};  // 右，下
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};    // 右，下，左，上
const std::vector<int> dy8 = { 0, -1, 0, 1, 1, -1, -1, 1 }, dx8 = { 1, 0, -1, 0, 1, 1, -1, -1 };

using namespace std;

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

    LL W, H, K;
    cin >> W >> H >> K;

    auto ys = make_v<int>(H, 0);
    auto xs = make_v<int>(W, 0);
    bool s_in_start = false;
    FOR(i, 0, K) {
        LL X, Y;
        cin >> X >> Y;
        X--; Y--;
        xs[X].emplace_back(Y);
        ys[Y].emplace_back(X);

        if (Y == 0 and X == 0) {
            s_in_start = true;
        }
    }
    ys[0].emplace_back(0);
    xs[0].emplace_back(0);
    ys[H - 1].emplace_back(W - 1);
    xs[W - 1].emplace_back(H - 1);

    unordered_map<LL, unordered_map<LL, vector<LL>>> y_graph, x_graph;
    FOR(y, 0, H) {
        sort(ALL(ys[y]));
        FOR(i, 0, ys[y].size()) {
            LL x = ys[y][i];

            if (i - 1 >= 0) {
                x_graph[y][x].emplace_back(ys[y][i - 1]);
            }
            if (i + 1 < ys[y].size()) {
                x_graph[y][x].emplace_back(ys[y][i + 1]);
            }
        }
    }
    FOR(x, 0, W) {
        sort(ALL(xs[x]));
        FOR(i, 0, xs[x].size()) {
            LL y = xs[x][i];

            if (i - 1 >= 0) {
                y_graph[x][y].emplace_back(xs[x][i - 1]);
            }
            if (i + 1 < xs[x].size()) {
                y_graph[x][y].emplace_back(xs[x][i + 1]);
            }
        }
    }

    priority_queue<tuple<LL, LL, LL>, vector<tuple<LL, LL, LL>>, greater<tuple<LL, LL, LL>>> que;
    que.emplace(make_tuple(0, 0, 0));

    vector<unordered_map<LL, LL>> cost(2);
    cost[0][0] = 0;
    LL ans = LINF;
    while (not que.empty()) {
        LL t, now, mode;
        tie(t, now, mode) = que.top(); que.pop();
        const LL y = now / W;
        const LL x = now % W;

        if (y == H - 1 and mode == 1) {
            chmin(ans, t + W - x - 1);
        }
        if (x == W - 1 and mode == 0) {
            chmin(ans, t + H - y - 1);
        }

        // スイッチ
        if ((y == 0 and x == 0 and s_in_start) or y != 0 or x != 0) {
            if (cost[1 - mode].find(y * W + x) == cost[1 - mode].end() or cost[1 - mode][y * W + x] > t + 1) {
                cost[1 - mode][y * W + x] = t + 1;
                que.emplace(make_tuple(t + 1, y * W + x, 1 - mode));
            }
        }

        // y軸ok
        if (mode == 0) {
            FOE(ny, y_graph[x][y]) {
                if (cost[mode].find(ny * W + x) == cost[mode].end() or cost[mode][ny * W + x] > t + abs(y - ny)) {
                    cost[mode][ny * W + x] = t + abs(y - ny);
                    que.emplace(make_tuple(t + abs(y - ny), ny * W + x, mode));
                }
            }
        }
        else {
            FOE(nx, x_graph[y][x]) {
                if (cost[mode].find(y * W + nx) == cost[mode].end() or cost[mode][y * W + nx] > t + abs(x - nx)) {
                    cost[mode][y * W + nx] = t + abs(x - nx);
                    que.emplace(make_tuple(t + abs(x - nx), y * W + nx, mode));
                }
            }
        }
    }

    if (ans == LINF) {
        print(-1);
    }
    else {
        print(ans);
    }

    return 0;
}




Measured memory_bytes: 88552