diff --git a/src/nodes/from_str.rs b/src/nodes/from_str.rs
index a589612..4608e48 100644
--- a/src/nodes/from_str.rs
+++ b/src/nodes/from_str.rs
@@ -22,6 +22,16 @@ enum ParsingState {
     ReadingNumber(usize),
 }
 
+impl Node {
+    fn from_name(s: &str) -> Result<Self, ()> {
+        Ok(match s {
+            "c" => Self::Number(Float::with_val(PREC, 299_792_458)),
+            "A" => Self::Number(Float::with_val(PREC, 6.02214076e23)),
+            f => Self::Function(f.parse()?),
+        })
+    }
+}
+
 impl FromStr for Nodes {
     type Err = Error;
     fn from_str(s: &str) -> Result<Self, Self::Err> {
@@ -55,11 +65,9 @@ impl FromStr for Nodes {
                 ParsingState::Start => {}
                 ParsingState::ReadingFunctionName(start_index) => {
                     if !c.is_alphabetic() {
-                        nodes.push(Node::Function(
-                            filtered_string[start_index..i].parse().map_err(|()| {
-                                Error::InvalidFunction(filtered_string[start_index..i].to_owned())
-                            })?,
-                        ));
+                        nodes.push(Node::from_name(&filtered_string[start_index..i]).map_err(
+                            |()| Error::InvalidFunction(filtered_string[start_index..i].to_owned()),
+                        )?);
 
                         state = ParsingState::Start;
                     }
@@ -107,11 +115,11 @@ impl FromStr for Nodes {
         match state {
             ParsingState::Start => {}
             ParsingState::ReadingFunctionName(start_index) => {
-                nodes.push(Node::Function(
-                    filtered_string[start_index..i].parse().map_err(|()| {
+                nodes.push(
+                    Node::from_name(&filtered_string[start_index..i]).map_err(|()| {
                         Error::InvalidFunction(filtered_string[start_index..i].to_owned())
                     })?,
-                ));
+                );
             }
             ParsingState::ReadingNumber(start_index) => {
                 nodes.push(Node::Number(