func minimumRecolors(blocks string, k int) int {
m := len(blocks)
for i:=0; i<len(blocks)-k+1; i++ {
c := 0
for j:=0; j<k; j++ {
if blocks[i+j] == 'W' {
c++
}
}
if c < m {
m = c
}
}
return m
}