#include <bits/stdc++.h>
// created [2019/12/23] 12:51:08
#pragma GCC diagnostic ignored "-Wsign-compare"
#pragma GCC diagnostic ignored "-Wsign-conversion"

using i32   = int32_t;
using i64   = int64_t;
using u32   = uint32_t;
using u64   = uint64_t;
using uint  = unsigned int;
using usize = std::size_t;
using ll    = long long;
using ull   = unsigned long long;
using ld    = long double;
template<typename T, usize n>
using arr = T (&)[n];
template<typename T, usize n>
using c_arr = const T (&)[n];
template<typename T> constexpr T popcount(const T u) { return u ? static_cast<T>(__builtin_popcountll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T log2p1(const T u) { return u ? static_cast<T>(64 - __builtin_clzll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T msbp1(const T u) { return log2p1(u); }
template<typename T> constexpr T lsbp1(const T u) { return __builtin_ffsll(u); }
template<typename T> constexpr T clog(const T u) { return u ? log2p1(u - 1) : static_cast<T>(u); }
template<typename T> constexpr bool ispow2(const T u) { return u and (static_cast<u64>(u) & static_cast<u64>(u - 1)) == 0; }
template<typename T> constexpr T ceil2(const T u) { return static_cast<T>(1) << clog(u); }
template<typename T> constexpr T floor2(const T u) { return u == 0 ? static_cast<T>(0) : static_cast<T>(1) << (log2p1(u) - 1); }
template<typename T> constexpr bool btest(const T mask, const usize ind) { return static_cast<bool>((static_cast<u64>(mask) >> ind) & static_cast<u64>(1)); }
template<typename T> void bset(T& mask, const usize ind) { mask |= (static_cast<T>(1) << ind); }
template<typename T> void breset(T& mask, const usize ind) { mask &= ~(static_cast<T>(1) << ind); }
template<typename T> void bflip(T& mask, const usize ind) { mask ^= (static_cast<T>(1) << ind); }
template<typename T> void bset(T& mask, const usize ind, const bool b) { (b ? bset(mask, ind) : breset(mask, ind)); }
template<typename T> constexpr T bcut(const T mask, const usize ind) { return ind == 0 ? static_cast<T>(0) : static_cast<T>((static_cast<u64>(mask) << (64 - ind)) >> (64 - ind)); }
template<typename T> bool chmin(T& a, const T& b) { return (a > b ? a = b, true : false); }
template<typename T> bool chmax(T& a, const T& b) { return (a < b ? a = b, true : false); }
constexpr unsigned int mod                  = 1000000007;
template<typename T> constexpr T inf_v      = std::numeric_limits<T>::max() / 4;
template<typename Real> constexpr Real pi_v = Real{3.141592653589793238462643383279502884};
auto mfp = [](auto&& f) { return [=](auto&&... args) { return f(f, std::forward<decltype(args)>(args)...); }; };

template<typename T>
T in()
{
    T v;
    return std::cin >> v, v;
}
template<typename T, typename Uint, usize n, usize i>
T in_v(typename std::enable_if<(i == n), c_arr<Uint, n>>::type) { return in<T>(); }
template<typename T, typename Uint, usize n, usize i>
auto in_v(typename std::enable_if<(i < n), c_arr<Uint, n>>::type& szs)
{
    const usize s = (usize)szs[i];
    std::vector<decltype(in_v<T, Uint, n, i + 1>(szs))> ans(s);
    for (usize j = 0; j < s; j++) { ans[j] = in_v<T, Uint, n, i + 1>(szs); }
    return ans;
}
template<typename T, typename Uint, usize n>
auto in_v(c_arr<Uint, n> szs) { return in_v<T, Uint, n, 0>(szs); }
template<typename... Types>
auto in_t() { return std::tuple<std::decay_t<Types>...>{in<Types>()...}; }
struct io_init
{
    io_init()
    {
        std::cin.tie(nullptr), std::ios::sync_with_stdio(false);
        std::cout << std::fixed << std::setprecision(20);
    }
    void clear()
    {
        std::cin.tie(), std::ios::sync_with_stdio(true);
    }
} io_setting;

template<typename T>
int out(const T& v) { return std::cout << v, 0; }
template<typename T>
int out(const std::vector<T>& v)
{
    for (usize i = 0; i < v.size(); i++) {
        if (i > 0) { std::cout << ' '; }
        out(v[i]);
    }
    return std::cout << "\n", 0;
}
template<typename T1, typename T2>
int out(const std::pair<T1, T2>& v) { return out(v.first), std::cout << ' ', out(v.second), 0; }
template<typename T, typename... Args>
int out(const T& v, const Args... args) { return out(v), std::cout << ' ', out(args...), 0; }
template<typename... Args>
int outln(const Args... args) { return out(args...), std::cout << '\n', 0; }
template<typename... Args>
void outel(const Args... args) { return out(args...), std::cout << std::endl, 0; }
#    define SHOW(...) static_cast<void>(0)
constexpr ull TEN(const usize n) { return n == 0 ? 1ULL : TEN(n - 1) * 10ULL; }

template<typename T, typename Uint, usize n, usize i>
auto make_v(typename std::enable_if<(i == n), c_arr<Uint, n>>::type, const T& v = T{}) { return v; }
template<typename T, typename Uint, usize n, usize i>
auto make_v(typename std::enable_if<(i < n), c_arr<Uint, n>>::type szs, const T& v = T{})
{
    const usize s = (usize)szs[i];
    return std::vector<decltype(make_v<T, Uint, n, i + 1>(szs, v))>(s, make_v<T, Uint, n, i + 1>(szs, v));
}
template<typename T, typename Uint, usize n>
auto make_v(c_arr<Uint, n> szs, const T& t = T{}) { return make_v<T, Uint, n, 0>(szs, t); }
int main()
{
    using pll    = std::pair<ll, ll>;
    const auto W = in<ll>(), H = in<ll>();
    auto enc     = [&](ll x, ll y) -> pll { return pll{x + y, y - x}; };
    auto dec     = [&](ll x, ll y) -> pll { return std::abs(x + y) % 2 == 1 ? pll{-1, -1} : pll{(x - y) / 2, (x + y) / 2}; };
    auto L1      = [&](ll x1, ll y1, ll x2, ll y2) { return std::abs(x1 - x2) + std::abs(y1 - y2); };
    auto is_in   = [&](ll x, ll y) { return 1 <= y and y <= H and 1 <= x and x <= W; };
    const auto N = in<int>();
    std::vector<ll> rxs(N), rys(N);
    for (int i = 0; i < N; i++) { rxs[i] = in<ll>(), rys[i] = in<ll>(); }
    {
        std::set<ll> parity;
        for (int i = 0; i < N; i++) { parity.insert(std::abs(rxs[i] + rys[i]) % 2); }
        if (parity.size() == 2) { return outln(0); }
    }
    std::vector<ll> xs(N), ys(N);
    for (int i = 0; i < N; i++) { std::tie(xs[i], ys[i]) = enc(rxs[i], rys[i]); }
    auto is_ok = [&](ll x, ll y) {
        if (not is_in(x, y)) { return false; }
        std::set<ll> ds;
        for (int i = 0; i < N; i++) { ds.insert(L1(rxs[i], rys[i], x, y)); }
        return ds.size() == 1;
    };
    const ll ym = *std::min_element(ys.begin(), ys.end());
    const ll xm = *std::min_element(xs.begin(), xs.end());
    const ll yM = *std::max_element(ys.begin(), ys.end());
    const ll xM = *std::max_element(xs.begin(), xs.end());
    ll ps[]     = {xm + (yM - ym) / 2, xM - (yM - ym) / 2, (xm + xM) / 2, (xm + xM) / 2};
    ll qs[]     = {(ym + yM) / 2, (ym + yM) / 2, yM - (xM - xm) / 2, ym + (xM - xm) / 2};
    for (int i = 0; i < 4; i++) { std::tie(ps[i], qs[i]) = dec(ps[i], qs[i]); }
    if (xm == xM) {
        if (not is_ok(ps[0], qs[0]) or not is_ok(ps[1], qs[1])) { return outln(0); }
        ll ans = (W - ps[0] + 1) * (H - qs[0] + 1) + ps[1] * qs[1];
        if (N == 2) { ans += (ps[0] - ps[1] - 1); }
        return outln(ans);
    }
    if (ym == yM) {
        if (not is_ok(ps[2], qs[2]) or not is_ok(ps[3], qs[3])) { return outln(0); }
        ll ans = (W - ps[2] + 1) * qs[2] + ps[3] * (H - qs[3] + 1);
        if (N == 2) { ans += (ps[2] - ps[3] - 1); }
        return outln(ans);
    }
    std::set<pll> start;
    for (int i = 0; i < 4; i++) {
        if (is_ok(ps[i], qs[i])) { start.insert({ps[i], qs[i]}); }
    }
    ll ans = start.size();
    if (start.size() == 1) {
        const auto [p, q] = *start.begin();
        constexpr ll dx[] = {-1, -1, -1, 0, 0, 1, 1, 1};
        constexpr ll dy[] = {-1, 0, 1, -1, 1, -1, 0, 1};
        for (int i = 0; i < 8; i++) {
            ll inf = 0, sup = H + W;
            while (sup - inf > 1) {
                const ll mid = (inf + sup) / 2;
                const ll np = p + mid * dx[i], nq = q + mid * dy[i];
                (is_ok(np, nq) ? inf : sup) = mid;
            }
            ans += inf;
        }
        return outln(ans);
    } else if (start.size() == 2) {
        const auto [p0, q0] = *start.begin();
        const auto [p1, q1] = *start.rbegin();
        constexpr ll dx[]   = {-1, -1, -1, 0, 0, 1, 1, 1};
        constexpr ll dy[]   = {-1, 0, 1, -1, 1, -1, 0, 1};
        for (int i = 0; i < 8; i++) {
            ll inf = 0, sup = H + W;
            while (sup - inf > 1) {
                const ll mid = (inf + sup) / 2;
                const ll np = p0 + mid * dx[i], nq = q0 + mid * dy[i];
                (is_ok(np, nq) and (np != p1 or nq != q1) ? inf : sup) = mid;
            }
            ans += inf;
        }
        for (int i = 0; i < 8; i++) {
            if (dx[i] != 0 and dy[i] != 0) { continue; }
            ll inf = 0, sup = H + W;
            while (sup - inf > 1) {
                const ll mid = (inf + sup) / 2;
                const ll np = p1 + mid * dx[i], nq = q1 + mid * dy[i];
                (is_ok(np, nq) ? inf : sup) = mid;
            }
            ans += inf;
        }
    }
    outln(ans);
    return 0;
}