Add stages and install bc.

Jenkinsfile

@@ -1,7 +1,7 @@
 node("linux && amd64 && docker") {
   docker.image("icedream/freetz@sha256:6607702228ee9ee819d888702acf3ddefe7609132f7f15c88349251a15f5a5cc").inside {
+    stage("Checkout") {
        checkout scm
-
        sh """
        cd ${pwd()}
        chown -R freetz:freetz .
@@ -9,7 +9,14 @@ node("linux && amd64 && docker") {
        cp -a freetz /
        cp -a .config config include make /freetz
        """
+    }
 
+    sh """
+    apt update
+    apt install -y bc
+    """
+
+    stage("Build") {
       ansiColor('xterm') {
         sh """
         cd /freetz
@@ -26,6 +33,7 @@ node("linux && amd64 && docker") {
         cp -r images outboard \"${env.WORKSPACE}\"
         """
       }
+    }
 
     archive "images/**,outboard/**"
   }