Go: package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

type Matrix struct {
	r int // num of row
	c int // num of column
}

type Range struct {
	start int // index, inclusive
	end   int // index, inclusive
}

func (r Range) length() int {
	return r.end - r.start + 1
}

func calcMultiplication(x, y Matrix) (Matrix, int) {
	if x.c != y.r {
		panic("cannnot calculate")
	}
	return Matrix{x.r, y.c}, x.r * y.c * x.c
}

func calcMinMatrixChainMultiplication(matrices []Matrix, r Range, memo map[Range]int) (Matrix, int) {
	if v, ok := memo[r]; ok {
		return Matrix{matrices[r.start].r, matrices[r.end].c}, v
	}
	if r.length() == 0 {
		panic("must not be empty")
	} else if r.length() == 1 {
		return matrices[r.start], 0
	}

	var minCount int = math.MaxInt32

	for i := 0; i < r.length()-1; i++ {
		formerRange := Range{r.start, r.start + i}
		latterRange := Range{r.start + i + 1, r.end}
		matF, countF := calcMinMatrixChainMultiplication(matrices, formerRange, memo)
		matL, countL := calcMinMatrixChainMultiplication(matrices, latterRange, memo)
		_, countFL := calcMultiplication(matF, matL)
		count := countF + countL + countFL
		if count < minCount {
			minCount = count
		}
	}
	memo[r] = minCount
	return Matrix{matrices[r.start].r, matrices[r.end].c}, minCount
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	n, _ := nextInt(sc)
	matrices := make([]Matrix, n)
	for i := 0; i < n; i++ {
		r, _ := nextInt(sc)
		c, _ := nextInt(sc)
		matrices[i] = Matrix{r, c}
	}
	memo := make(map[Range]int)
	_, resultCount := calcMinMatrixChainMultiplication(matrices, Range{0, len(matrices) - 1}, memo)
	fmt.Println(resultCount)
}

func nextInt(sc *bufio.Scanner) (int, error) {
	sc.Scan()
	return strconv.Atoi(sc.Text())
}

C++: /**
 * @copyright (c) 2020 Daisuke Hashimoto
 */

#include <cstdint>
#include <iostream>
#include <string>
#include <algorithm>

constexpr int32_t kMaxNumberOfMatrices = 100;
constexpr int32_t kMaxNumberOfRowsAndCols = 100;

void CallMatrixChainMultiplication(std::istream &input_stream);

struct Matrix {
  int32_t number_of_rows{0};
  int32_t number_of_columns{0};
};

struct LookUp {
  bool calculated{false};
  int32_t mcm{INT32_MAX};
};

class MatrixChainMultiplication {
 public:
  MatrixChainMultiplication() noexcept;
  ~MatrixChainMultiplication() noexcept;

  void AddMatrix(const int32_t number_of_rows, const int32_t number_of_columns);
  int32_t CalculateMinMultiplyCount();

  static int32_t GetMultiplyCount(const Matrix &a, const Matrix &b);
  static Matrix GetMultipliedMatrix(const Matrix &a, const Matrix &b);
  static Matrix GenerateMatrix(const int32_t number_of_rows, const int32_t number_of_columns);

 private:
  int32_t CalculateMcmRecursively(const int32_t start, const int32_t end);
  bool IsInvalidIndex(const int32_t index) const noexcept;
  bool IsInvalidArg(const int32_t start, const int32_t end) const noexcept;
  bool IsAlreadyCalculated(const int32_t start, const int32_t end) const;
  int32_t GetCalculatedResult(const int32_t start, const int32_t end) const;
  void StoreCalculatedResult(const int32_t start, const int32_t end, const int32_t mcm);

  MatrixChainMultiplication(const MatrixChainMultiplication &obj) = delete;
  MatrixChainMultiplication &operator=(const MatrixChainMultiplication &obj) = delete;
  MatrixChainMultiplication(MatrixChainMultiplication &&obj) = delete;
  MatrixChainMultiplication &operator=(MatrixChainMultiplication &&obj) = delete;

 private:
  int32_t number_of_matrices_;
  Matrix matrices_[kMaxNumberOfMatrices];
  LookUp look_up_table_[kMaxNumberOfMatrices][kMaxNumberOfMatrices];
};

void CallMatrixChainMultiplication(std::istream &input_stream) {
  input_stream.tie(0);
  std::ios::sync_with_stdio(false);
  MatrixChainMultiplication *matrix_chain_multiplication = new MatrixChainMultiplication();
  try {
    int32_t number_of_matrices;
    input_stream >> number_of_matrices;
    for (int32_t i = 0; i < number_of_matrices; ++i) {
      int32_t number_of_rows, number_of_columns;
      input_stream >> number_of_rows >> number_of_columns;
      matrix_chain_multiplication->AddMatrix(number_of_rows, number_of_columns);
    }
    const int32_t multiply_count = matrix_chain_multiplication->CalculateMinMultiplyCount();
    std::cout << multiply_count << std::endl;
  } catch (...) {
    std::cerr << "ERROR: CallMatrixChainMultiplication()" << std::endl;
    throw;
  }
  delete matrix_chain_multiplication;
}

// ****************************************************

MatrixChainMultiplication::MatrixChainMultiplication() noexcept : number_of_matrices_(0) {}

MatrixChainMultiplication::~MatrixChainMultiplication() noexcept {}

void MatrixChainMultiplication::AddMatrix(const int32_t number_of_rows, const int32_t number_of_columns) {
  if (number_of_matrices_ >= kMaxNumberOfMatrices) {
    std::cerr << "ERROR: AddMatrix(): Number of matricis size exceeded a limit = " << kMaxNumberOfMatrices << std::endl;
    throw 1;
  }
  const int32_t store_index = number_of_matrices_;
  ++number_of_matrices_;
  matrices_[store_index] = GenerateMatrix(number_of_rows, number_of_columns);
}

int32_t MatrixChainMultiplication::CalculateMinMultiplyCount() {
  const int32_t count = CalculateMcmRecursively(0, number_of_matrices_ - 1);
  return count;
}

int32_t MatrixChainMultiplication::CalculateMcmRecursively(const int32_t start, const int32_t end) {
  int32_t mcm;
  if (start == end) {
    mcm = 0;
  } else if (IsInvalidArg(start, end)) {
    std::cerr << "ERROR: CalculateMcmRecursively(): Invalid arg start = " << start << ", end = " << end << std::endl;
    throw 1;
  } else {
    try {
      if (IsAlreadyCalculated(start, end)) {
        mcm = GetCalculatedResult(start, end);
      } else {
        mcm = INT32_MAX;
        for (int32_t i = start; i <= end - 1; ++i) {
          const int32_t temp_mcm =
              matrices_[start].number_of_rows * matrices_[i].number_of_columns * matrices_[end].number_of_columns +
              CalculateMcmRecursively(start, i) + CalculateMcmRecursively(i + 1, end);
          mcm = std::min(mcm, temp_mcm);
        }
        StoreCalculatedResult(start, end, mcm);
      }
    } catch (...) {
      std::cerr << "ERROR: CalculateMcmRecursively()" << std::endl;
      throw;
    }
  }
  return mcm;
}

bool MatrixChainMultiplication::IsInvalidIndex(const int32_t index) const noexcept {
  return ((index < 0) || (index > number_of_matrices_));
}

bool MatrixChainMultiplication::IsInvalidArg(const int32_t start, const int32_t end) const noexcept {
  const bool is_invalid_start = IsInvalidIndex(start);
  const bool is_invalid_end = IsInvalidIndex(end);
  const bool is_invalid_order = (start > end);
  return is_invalid_start || is_invalid_end || is_invalid_order;
}

bool MatrixChainMultiplication::IsAlreadyCalculated(const int32_t start, const int32_t end) const {
  if (IsInvalidArg(start, end)) {
    std::cerr << "ERROR: IsAlreadyCalculated(): start = " << start << ", end = " << end << std::endl;
    throw 1;
  }
  return look_up_table_[start][end].calculated;
}

int32_t MatrixChainMultiplication::GetCalculatedResult(const int32_t start, const int32_t end) const {
  if (IsInvalidArg(start, end)) {
    std::cerr << "ERROR: GetCalculatedResult(): start = " << start << ", end = " << end << std::endl;
    throw 1;
  }
  return look_up_table_[start][end].mcm;
}

void MatrixChainMultiplication::StoreCalculatedResult(const int32_t start, const int32_t end, const int32_t mcm) {
  if (IsInvalidArg(start, end)) {
    std::cerr << "ERROR: GetCalculatedResult(): start = " << start << ", end = " << end << std::endl;
    throw 1;
  }
  look_up_table_[start][end].mcm = mcm;
  look_up_table_[start][end].calculated = true;
}

int32_t MatrixChainMultiplication::GetMultiplyCount(const Matrix &a, const Matrix &b) {
  if (a.number_of_columns != b.number_of_rows) {
    std::cerr << "ERROR: GetMultiplyCount(): Invalid a.number_of_columns = " << a.number_of_columns
              << ", b.number_of_rows = " << b.number_of_rows << std::endl;
    throw 1;
  }
  return a.number_of_rows * a.number_of_columns * b.number_of_columns;
}

Matrix MatrixChainMultiplication::GetMultipliedMatrix(const Matrix &a, const Matrix &b) {
  if (a.number_of_columns != b.number_of_rows) {
    std::cerr << "ERROR: GetMultipliedMatrix(): Invalid a.number_of_columns = " << a.number_of_columns
              << ", b.number_of_rows = " << b.number_of_rows << std::endl;
    throw 1;
  }
  const Matrix result = GenerateMatrix(a.number_of_rows, b.number_of_columns);
  return result;
}

Matrix MatrixChainMultiplication::GenerateMatrix(const int32_t number_of_rows, const int32_t number_of_columns) {
  Matrix mat;
  mat.number_of_rows = number_of_rows;
  mat.number_of_columns = number_of_columns;
  return mat;
}

int main(int argc, char *argv[]) {
  try {
    CallMatrixChainMultiplication(std::cin);
  } catch (...) {
    std::cerr << "ERROR: main()" << std::endl;
  }
  return 0;
}