I cant figure out this on C$++$

Given an integer N$,$ which represents aggregate of marks obtained by a student, find the grade according to the marks obtained$($Use Ladder if$-$else$).$

if $90<=$ N$,$ grade obtained is $\text{'}$A$\text{'}.$

if $60<=$ N $<=89,$ grade obtained is $\text{'}$B$\text{'}.$

if $30<=$ N $<=59,$ grade obtained is $\text{'}$C$\text{'}.$

if N $<30,$ grade obtained is $\text{'}$D$\text{'}.$

Example Input: $35$

where:

First line represents the aggregate of marks obtained by the students.

Output:

C

As the aggregate of the marks lie in the range $30<=$ N $<=59,$ grade obtained is $\text{'}$C$\text{'}.$

Value of N can be in the range $0$ to $100.$