diff --git a/README.md b/README.md
index 79af9274..6550edc0 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,18 @@ $ bundle exec lrama --version
 $ lrama -d sample/parse.y
 ```
 
+```shell
+# "calc", "calc.c", and "calc.h" are generated
+$ lrama -d sample/calc.y -o calc.c && gcc -Wall calc.c -o calc && ./calc
+Enter the formula:
+1
+=> 1
+1+2*3
+=> 7
+(1+2)*3
+=> 9
+```
+
 ## Build Ruby
 
 1. Install Lrama
diff --git a/sample/calc.y b/sample/calc.y
index cbd553d0..c03d6adf 100644
--- a/sample/calc.y
+++ b/sample/calc.y
@@ -92,6 +92,7 @@ static int yyerror(YYLTYPE *loc, const char *str) {
 }
 
 int main() {
+    printf("Enter the formula:\n");
     yyparse();
     return 0;
 }