diff --git a/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/Cargo.toml b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/Cargo.toml
new file mode 100644
index 0000000..e87a33d
--- /dev/null
+++ b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "is_johnny_making_progress"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/lib.rs b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/lib.rs
new file mode 100644
index 0000000..fe3a784
--- /dev/null
+++ b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/lib.rs
@@ -0,0 +1,11 @@
+pub fn progress_days(days: &'static [usize]) -> usize {
+    let mut progress_days = 0;
+
+    for i in 1..days.len() {
+        if days[i] > days[i-1] {
+            progress_days += 1;
+        }
+    }
+
+    progress_days
+}
diff --git a/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/main.rs b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/main.rs
new file mode 100644
index 0000000..a15d23e
--- /dev/null
+++ b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/src/main.rs
@@ -0,0 +1,3 @@
+fn main() {
+    println!("Run `cargo test`.");
+}
diff --git a/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/tests/progress_days_tests.rs b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/tests/progress_days_tests.rs
new file mode 100644
index 0000000..609c4d0
--- /dev/null
+++ b/Week-01/Day-04_Is-Johnny-Making-Progress/is_johnny_making_progress/tests/progress_days_tests.rs
@@ -0,0 +1,21 @@
+use is_johnny_making_progress::progress_days;
+
+#[test]
+fn no_progress_days() {
+    assert_eq!(progress_days(&[9, 9]), 0);
+}
+
+#[test]
+fn one_progress_day() {
+    assert_eq!(progress_days(&[6, 5, 4, 3, 2, 9]), 1);
+}
+
+#[test]
+fn two_progress_days() {
+    assert_eq!(progress_days(&[3, 4, 1, 2]), 2);
+}
+
+#[test]
+fn three_progress_days() {
+    assert_eq!(progress_days(&[10, 11, 12, 9, 10]), 3);
+}