planting grapevines

vineyard owner needs to know how many grapevines to plant per row.
in addition to grapevines each row has a trellis end-post assembly.
use the following formula to calculate how many vines will fit in a row:
V = (R - (2*E)) / S

V - number of grapevines that will fit in a row
R - length of row in meters
E - space, in meters, of by end-post assembly
S - space between vines in meters

program should accept the following as input:
1. length of row in meters
2. space used by end-post assembly in meters
3. space between the each vine in meters

after data is input the program should calculate and display the number of vines that will fit in a row (can you plant a fraction of a vine??)