diff --git a/include/s0509_fibonacci_number.hpp b/include/s0509_fibonacci_number.hpp
new file mode 100644
index 0000000..8d60efb
--- /dev/null
+++ b/include/s0509_fibonacci_number.hpp
@@ -0,0 +1,13 @@
+#ifndef S0509_FIBONACCI_NUMBER_HPP
+#define S0509_FIBONACCI_NUMBER_HPP
+
+#include <vector>
+
+using namespace std;
+
+class S0509 {
+ public:
+  int fib(int n);
+};
+
+#endif
diff --git a/src/s0509_fibonacci_number.cpp b/src/s0509_fibonacci_number.cpp
new file mode 100644
index 0000000..872b50e
--- /dev/null
+++ b/src/s0509_fibonacci_number.cpp
@@ -0,0 +1,9 @@
+#include "s0509_fibonacci_number.hpp"
+
+int S0509::fib(int n) {
+  vector<int> dp{0, 1};
+  for (int i{2}; i <= n; ++i) {
+    dp.push_back(dp[i - 1] + dp[i - 2]);
+  }
+  return dp[n];
+}
diff --git a/tests/s0509_fibonacci_number.cpp b/tests/s0509_fibonacci_number.cpp
new file mode 100644
index 0000000..477cee4
--- /dev/null
+++ b/tests/s0509_fibonacci_number.cpp
@@ -0,0 +1,24 @@
+#include "s0509_fibonacci_number.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem509, Case1) {
+  int n{2};
+  int expected{1};
+  S0509 solution;
+  EXPECT_EQ(solution.fib(n), expected);
+}
+
+TEST(Problem509, Case2) {
+  int n{3};
+  int expected{2};
+  S0509 solution;
+  EXPECT_EQ(solution.fib(n), expected);
+}
+
+TEST(Problem509, Case3) {
+  int n{4};
+  int expected{3};
+  S0509 solution;
+  EXPECT_EQ(solution.fib(n), expected);
+}