#include<mpi.h>
#pragma TASS input
int N_BOUND;
#pragma TASS input {0<=N && N<=N_BOUND}
int N; 
int myrank;
int nprocs;
int left;
int right;

void main() {
  int argc;
  char **argv;
  int i;
	
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
  left = (myrank+nprocs-1)%nprocs;
  right = (myrank+nprocs+1)%nprocs;
  i=0;
#pragma TASS collective invariant L i==PROC[right]@main.i;
  while (i<N) {
    if (myrank%2==0) {
      MPI_Send(NULL, 0, MPI_INT, right, 0, MPI_COMM_WORLD);
      MPI_Recv(NULL, 0, MPI_INT, left, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    } else {
      MPI_Recv(NULL, 0, MPI_INT, left, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
      MPI_Send(NULL, 0, MPI_INT, right, 0, MPI_COMM_WORLD);
    }
    i++;
  }
  MPI_Finalize();
}