diff --git a/interpreter.cpp b/interpreter.cpp
index 1543d6e..3a3d2e6 100644
--- a/interpreter.cpp
+++ b/interpreter.cpp
@@ -121,7 +121,9 @@ void interpreter::exec_instruction(const std::string& code, bool& done) {
     else if (code == "fun") fun();
     else if (code == "ret") ret();
     else if (code == "enl") enl();
-    else if (code == "out") out(); // for debugging
+    else if (code == "inp") inp();
+    else if (code == "out") out();
+    else if (code == "err") err();
     else throw syntax_error {code};
 }
 
@@ -387,7 +389,19 @@ void interpreter::ret() {
 
 // debugging --------------------------------------------------------------
 
+void interpreter::inp() {
+    std::string val;
+    std::cin >> val;
+    _stack.push_back(val);
+    _pc++;
+}
+
 void interpreter::out() {
     std::cout << _stack.back() << '\n';
     _pc++;
 }
+
+void interpreter::err() {
+    std::cerr << _stack.back() << '\n';
+    _pc++;
+}
diff --git a/interpreter.hpp b/interpreter.hpp
index d042f03..c5b5f77 100644
--- a/interpreter.hpp
+++ b/interpreter.hpp
@@ -72,8 +72,10 @@ class interpreter {
         void fun();
         void ret();
 
-        // debugging
+        // I/O
+        void inp();
         void out();
+        void err();
 };
 
 #endif // _interpreter_H_