diff --git a/exercise4/wave_2d_parallel.c b/exercise4/wave_2d_parallel.c
index ca0c692..bffb5ef 100644
--- a/exercise4/wave_2d_parallel.c
+++ b/exercise4/wave_2d_parallel.c
@@ -14,7 +14,7 @@
 // TASK: T1a
 // Include the MPI headerfile
 // BEGIN: T1
-;
+#include <mpi.h>
 // END: T1a
 
 // Convert 'struct timeval' into seconds in double prec. floating point
@@ -34,6 +34,11 @@ real_t
 #define U_prv(i, j) buffers[0][((i) + 1) * (N + 2) + (j) + 1]
 #define U(i, j) buffers[1][((i) + 1) * (N + 2) + (j) + 1]
 #define U_nxt(i, j) buffers[2][((i) + 1) * (N + 2) + (j) + 1]
+
+int world_size;
+int world_rank;
+
+#define ROOT 0
 // END: T1b
 
 // Simulation parameters: size, step count, and how often to save the state
@@ -243,7 +248,9 @@ int main(int argc, char **argv) {
   // TASK: T1c
   // Initialise MPI
   // BEGIN: T1c
-  ;
+  MPI_Init(&argc, &argv);
+  MPI_Comm_size(MPI_COMM_WORLD, &world_size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
   // END: T1c
 
   // TASK: T3
@@ -278,7 +285,7 @@ int main(int argc, char **argv) {
   // TASK: T1d
   // Finalise MPI
   // BEGIN: T1d
-  ;
+  MPI_Finalize();
   // END: T1d
 
   exit(EXIT_SUCCESS);