#include <stdio.h>
#include <mpi.h>

#define N 1000000

int main(int argc, char** argv) {
    int rank, size;

    /* initialize MPI */
    MPI_Init(&argc, &argv);

    /* get the rank (process id) and size (number of processes) */
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    /* have process 0 do many sends */
    if (rank == 0) {
        for (int i = 0; i < N; i++) {
            for (int j = 1; j < size; j++) {
                MPI_Send(&i, 1, MPI_INT, j, 0, MPI_COMM_WORLD);
            }
        }
    }

    /* have the rest receive that many values */
    else {
        for (int i = 0; i < N; i++) {
            int value;
            MPI_Recv(&value, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
        }
    }

    /* quit MPI */
    MPI_Finalize();
    return 0;
}