find difference between numbers

hi everybody i start work with matlab from short time and i need yours helps i try to find the difference between five distances i.e if i have r1=5,r2=7,r3=9,r4=13,r5=18 and try to find the difference between r2-r1,r3-r2 ,.....,r5-r4 and write this code to work with for but it is not work the code is

a=[5,7,9,13,18]
for i=1:5
r(i)=a(i+1)-a(i)
end

i get this error

Attempted to access a(6); index out of bounds because numel(a)=5.

thanks

Answer 1

[Walter Roberson]

 for i=1:4

Answer 2

[abbas hasan]

thanks it work correct