Sample program for lab 4

Revision:
2:fcf30b3e1c14
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed_app.json	Thu Feb 22 17:05:45 2018 +0000
@@ -0,0 +1,7 @@
+{
+    "config": {
+        "main-stack-size": {
+            "value": 2000
+        }
+    }
+}
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