#include <mpi.h>
#include <stdio.h>
int main(int argc, char **argv) {
    MPI_Init(&argc, &argv);
    int rank, size, len;
    char host[MPI_MAX_PROCESSOR_NAME];
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Get_processor_name(host, &len);

    double local = rank + 1.0, total;
    MPI_Reduce(&local, &total, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

    printf("rank %d of %d on %s\n", rank, size, host);
    if (rank == 0) printf("sum over ranks = %.0f\n", total);
    MPI_Finalize();
    return 0;
}