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

int main(int argc, char **argv)
{
    int rank, size;
    int i, j;
    
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    for (i = 0; i < size; ++i) {
        if (i == rank) {
            for (j = 0; j < size; ++j) {
                if (j == rank)
                    continue;
                printf("recv from %d\n", j);
                MPI_Recv(NULL, 0, MPI_INT, j, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            }
        } else {
            printf("send to %d\n", i);
            MPI_Send(NULL, 0, MPI_INT, i, 0, MPI_COMM_WORLD);
        }
    }

    MPI_Finalize();
    return 0;
}