#line 1 "E.cpp"
#include <algorithm>
#include <cstdint>
#include <vector>

#line 1 "~/git/library/utility/io.cpp"



/**
 * @brief 入出力
 * @author えびちゃん
 */

#include <cstddef>
#include <cctype>
#include <iomanip>
#include <iostream>
#include <tuple>
#include <utility>

class format {
public:
  using size_type = size_t;

private:
  char const* M_fmt;
  size_type M_nvars = 0;
  size_type M_error = -1;

  void M_print(std::ostream& os, char const* pos) const {
    while (*pos) {
      if (*pos == '{' || *pos == '}') ++pos;
      os << *pos++;
    }
  }

  template <typename Tp, typename... Args>
  void M_print(std::ostream& os, char const* pos, Tp const& x, Args const&... xs) const {
    while (true) {
      if (*pos == '{') {
        if (pos[1] == '{') {
          ++pos;
          os << '{';
        } else {
          char const* next = M_print_formatted(os, pos, x);
          return M_print(os, next, xs...);
        }
      } else {
        if (*pos == '}') ++pos;
        os << *pos;
      }
      ++pos;
    }
    char const* next = M_print_formatted(os, pos, x);
    M_print(os, next, xs...);
  }

  template <typename Tp>
  char const* M_print_formatted(std::ostream& os, char const* pos, Tp const& x) const {
    // parse flags, preferably
    while (*++pos != '}') {}
    os << x;
    return ++pos;
  }

  void M_scan(std::istream& is, char const* pos) const {
    while (true) {
      if (*pos == '{' || *pos == '}') ++pos;
      if (isspace(*pos)) {
        while (isspace(is.peek())) is.get();
      } else {
        if (is.peek() == *pos) {
          ++pos;
          is.get();
        } else {
          return;
        }
      }
    }
  }

  template <typename Tp, typename... Args>
  void M_scan(std::istream& is, char const* pos, Tp& x, Args&&... xs) const {
    while (true) {
      if (*pos == '{') {
        if (pos[1] == '{') {
          if (is.peek() == '{') {
            ++pos;
            is.get();
          } else {
            return;
          }
        } else {
          char const* next = M_scan_formatted(is, pos, x);
          return M_scan(is, next, xs...);
        }
      } else if (isspace(*pos)) {
        while (isspace(is.peek())) is.get();
        ++pos;
      } else {
        if (*pos == '}') ++pos;
        if (is.peek() == *pos) {
          ++pos;
          is.get();
        } else {
          return;
        }
      }
    }
  }

  template <typename Tp>
  char const* M_scan_formatted(std::istream& is, char const* pos, Tp& x) const {
    // parse flags, preferably
    while (*++pos != '}') {}
    is >> x;
    return ++pos;
  }

public:
  constexpr format(char const* fmt): M_fmt(fmt) {
    bool opens = 0;
    size_type i = 0;
    for (; fmt[i]; ++i) {
      if (fmt[i] == '{') {
        if (fmt[i+1] == '{') { ++i; continue; }  // escaped
        if (opens) { M_error = i; return; }
        opens = true;
      } else if (fmt[i] == '}') {
        if (fmt[i+1] == '}') { ++i; continue; }  // escaped
        if (!opens) { M_error = i; return; }
        opens = false;
        ++M_nvars;
      }
    }
    if (opens) { M_error = i; return; }
  }

  template <typename... Args>
  void print_(std::ostream& os, Args const&... xs) const {
    M_print(os, M_fmt, xs...);
  }

  template <typename... Args>
  void scan_(std::istream& is, Args&&... xs) const {
    M_scan(is, M_fmt, xs...);
  }

  constexpr size_type count() const { return M_nvars; }
  constexpr size_type error() const { return M_error; }
};

#define VA_COUNT(...)                                           \
  std::tuple_size<decltype(std::make_tuple(__VA_ARGS__))>::value

#define fprint(os, fmt, ...) (void)({                           \
      constexpr format fmt_(fmt);                               \
      constexpr size_t lhs = fmt_.count();                      \
      constexpr size_t rhs = VA_COUNT(__VA_ARGS__);             \
      static_assert(lhs == rhs, "size mismatch");               \
      static_assert(fmt_.error()+1 == 0, "misformatted");       \
      fmt_.print_(os, ##__VA_ARGS__);                           \
    })

#define fprintln(os, fmt, ...) (void)({         \
      fprint(os, fmt, ##__VA_ARGS__);           \
      os << '\n';;                              \
    })

#define print(...) fprint(std::cout, ##__VA_ARGS__)
#define println(...) fprintln(std::cout, ##__VA_ARGS__)
#define eprint(...) fprint(std::cerr, ##__VA_ARGS__)
#define eprintln(...) fprintln(std::cerr, ##__VA_ARGS__)

#define fscan(is, fmt, ...) (void)({                            \
      constexpr format fmt_(fmt);                               \
      constexpr size_t lhs = fmt_.count();                      \
      constexpr size_t rhs = VA_COUNT(__VA_ARGS__);             \
      static_assert(lhs == rhs, "size mismatch");               \
      static_assert(fmt_.error()+1 == 0, "misformatted");       \
      fmt_.scan_(is, ##__VA_ARGS__);                            \
    })

#define scan(...) fscan(std::cin, __VA_ARGS__)

__attribute__((constructor))
void ioinit() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cerr.tie(nullptr);
  std::cout << std::fixed << std::setprecision(16);
}


#line 1 "~/git/library/utility/literals.cpp"



/**
 * @brief ユーザ定義リテラル
 * @author えびちゃん
 */

#line 11 "~/git/library/utility/literals.cpp"

constexpr intmax_t  operator ""_jd(unsigned long long n) { return n; }
constexpr uintmax_t operator ""_ju(unsigned long long n) { return n; }
constexpr size_t    operator ""_zu(unsigned long long n) { return n; }
constexpr ptrdiff_t operator ""_td(unsigned long long n) { return n; }

constexpr int8_t   operator ""_i8(unsigned long long n)  { return n; }
constexpr int16_t  operator ""_i16(unsigned long long n) { return n; }
constexpr int32_t  operator ""_i32(unsigned long long n) { return n; }
constexpr int64_t  operator ""_i64(unsigned long long n) { return n; }
constexpr uint8_t  operator ""_u8(unsigned long long n)  { return n; }
constexpr uint16_t operator ""_u16(unsigned long long n) { return n; }
constexpr uint32_t operator ""_u32(unsigned long long n) { return n; }
constexpr uint64_t operator ""_u64(unsigned long long n) { return n; }


#line 1 "~/git/library/utility/make/vector.cpp"



/**
 * @brief 多次元 vector の作成
 * @author えびちゃん
 */

#line 10 "~/git/library/utility/make/vector.cpp"
#include <type_traits>
#line 12 "~/git/library/utility/make/vector.cpp"

namespace detail {
  template <typename Tp, size_t Nb>
  auto make_vector(std::vector<size_t>& sizes, Tp const& x) {
    if constexpr (Nb == 1) {
      return std::vector(sizes[0], x);
    } else {
      size_t size = sizes[Nb-1];
      sizes.pop_back();
      return std::vector(size, make_vector<Tp, Nb-1>(sizes, x));
    }
  }
}  // detail::

template <typename Tp, size_t Nb>
auto make_vector(size_t const(&sizes)[Nb], Tp const& x = Tp()) {
  std::vector<size_t> s(Nb);
  for (size_t i = 0; i < Nb; ++i) s[i] = sizes[Nb-i-1];
  return detail::make_vector<Tp, Nb>(s, x);
}


#line 1 "~/git/library/utility/set_if.cpp"



/**
 * @brief 条件つき代入
 * @author えびちゃん
 */

#line 10 "~/git/library/utility/set_if.cpp"

template <typename Tp>
bool set_if_less(Tp& dst, Tp const& src) {
  if (src < dst) return (dst = src), true;
  return false;
}

template <typename Tp>
bool set_if_greater(Tp& dst, Tp const& src) {
  if (dst < src) return (dst = src), true;
  return false;
}


#line 9 "E.cpp"

int main() {
  size_t r, c, k;
  scan("{} {} {}", r, c, k);

  auto a = make_vector({r+1, c+1}, 0_i64);
  for (size_t i = 0; i < k; ++i) {
    size_t ri, ci;
    int64_t vi;
    scan("{} {} {}", ri, ci, vi);
    --ri, --ci;
    a[ri][ci] = vi;
  }

  int64_t const inf = 1e18;
  auto dp = make_vector({5_zu, r+1, c+1}, -inf);

  dp[0][0][0] = 0;
  dp[1][0][0] = a[0][0];
  for (size_t i = 0; i < r; ++i) {
    for (size_t j = 0; j < c; ++j) {
      for (size_t h = 0; h <= 3; ++h) {
        {
          // >
          set_if_greater(dp[h+1][i][j+1], dp[h][i][j] + a[i][j+1]);
          set_if_greater(dp[h][i][j+1], dp[h][i][j]);
        }
        {
          // v
          set_if_greater(dp[1][i+1][j], dp[h][i][j] + a[i+1][j]);
          set_if_greater(dp[0][i+1][j], dp[h][i][j]);
        }
      }
    }
  }

  int64_t res = -inf;
  for (size_t h = 0; h <= 3; ++h)
    for (size_t i = 0; i < r; ++i)
      for (size_t j = 0; j < c; ++j)
        res = std::max(res, dp[h][i][j]);

  println("{}", res);
}


Measured memory_bytes: 495984