diff --git a/10_fibonacci/fibonacci.js b/10_fibonacci/fibonacci.js
index bb2c8cc..2279b0f 100644
--- a/10_fibonacci/fibonacci.js
+++ b/10_fibonacci/fibonacci.js
@@ -1,6 +1,19 @@
-const fibonacci = function() {
+const fibonacci = function (index) {
+  if (index < 0) return 'OOPS'
 
-};
+  // in loop, add up the sequence until the length of the array is index - 1
+  let seq = [1]
+
+  while (seq.length < index) {
+    if (seq.length === 1) {
+      seq.push(1)
+    } else {
+      seq.push(seq.at(-1) + seq.at(-2))
+    }
+  }
+
+  return seq.pop()
+}
 
 // Do not edit below this line
-module.exports = fibonacci;
+module.exports = fibonacci
diff --git a/10_fibonacci/fibonacci.spec.js b/10_fibonacci/fibonacci.spec.js
index 7f62213..49c341c 100644
--- a/10_fibonacci/fibonacci.spec.js
+++ b/10_fibonacci/fibonacci.spec.js
@@ -2,30 +2,30 @@ const fibonacci = require('./fibonacci')
 
 describe('fibonacci', () => {
   test('4th fibonacci number is 3', () => {
-    expect(fibonacci(4)).toBe(3);
-  });
-  test.skip('6th fibonacci number is 8', () => {
-    expect(fibonacci(6)).toBe(8);
-  });
-  test.skip('10th fibonacci number is 55', () => {
-    expect(fibonacci(10)).toBe(55);
-  });
-  test.skip('15th fibonacci number is 610', () => {
-    expect(fibonacci(15)).toBe(610);
-  });
-  test.skip('25th fibonacci number is 75025', () => {
-    expect(fibonacci(25)).toBe(75025);
-  });
-  test.skip('doesn\'t accept negatives', () => {
-    expect(fibonacci(-25)).toBe("OOPS");
-  });
-  test.skip('DOES accept strings', () => {
-    expect(fibonacci("1")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(fibonacci("2")).toBe(1);
-  });
-  test.skip('DOES accept strings', () => {
-    expect(fibonacci("8")).toBe(21);
-  });
-});
+    expect(fibonacci(4)).toBe(3)
+  })
+  test('6th fibonacci number is 8', () => {
+    expect(fibonacci(6)).toBe(8)
+  })
+  test('10th fibonacci number is 55', () => {
+    expect(fibonacci(10)).toBe(55)
+  })
+  test('15th fibonacci number is 610', () => {
+    expect(fibonacci(15)).toBe(610)
+  })
+  test('25th fibonacci number is 75025', () => {
+    expect(fibonacci(25)).toBe(75025)
+  })
+  test('doesn\'t accept negatives', () => {
+    expect(fibonacci(-25)).toBe('OOPS')
+  })
+  test('DOES accept strings', () => {
+    expect(fibonacci('1')).toBe(1)
+  })
+  test('DOES accept strings', () => {
+    expect(fibonacci('2')).toBe(1)
+  })
+  test('DOES accept strings', () => {
+    expect(fibonacci('8')).toBe(21)
+  })
+})