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

void main(int argc, char *argv[])
{
  double fdisp, fsample, fsource, n;

  if (argc < 4) {
    fprintf(stderr, "Usage: %s N f_sample f_disp\n", argv[0]);
    fprintf(stderr, "Program calculates f_source = N * f_sample - f_disp \n");
    exit(1);
  }

  n       = atof(argv[1]);
  fsample = atof(argv[2]);
  fdisp   = atof(argv[3]);

  fsource = n * fsample - fdisp;
  printf("f_source = %20.9f\n", fsource);
}