Sum of Maximum of continuous blocks of length k

Question

Given a array of N elements and a number k, then find the sum of maximum of a all continuous blocks of length k?

Examples :

1. A = {2,5,2}, k = 2, Max for 1st block = 5, 2nd block = 5, So sum is 10.
2. A = {3,1,8}, k = 2, Max for 1st block = 3, 2nd block = 8, So sum is 11.
3. A = {2,5,2}, k = 1, Max for 1st block = 2, 2nd block = 5, third block = 2. So sum is 9.
4. A = {2,5,2}, k = 3, Max for only block = 5. So sum is 5.