diff --git a/exercise1/plot_image.sh b/exercise1/plot_image.sh
old mode 100644
new mode 100755
diff --git a/flake.nix b/flake.nix
index 63a4851..c994221 100644
--- a/flake.nix
+++ b/flake.nix
@@ -16,14 +16,15 @@
         buildInputs = with pkgs; [
           gcc
           gnumake
-          feh
-          feh
           imagemagick_light
           typst
           typstyle
           zip
           unzip
           feh
+          # exercise 1: 1D wave equation plotting utils
+          gnuplot
+          ffmpeg
         ];
         shellHook = ''
           echo welcome!