n=gets.to_i
s=gets.chomp
ans=0
0.upto(n-3){|i|
  next unless s[i]==?U
  (i+2).upto(n-1){|k|
    next unless s[k]==?G
    next if (i+k).odd?
    ans+=1 if s[(i+k)/2]==?M
  }
}

puts ans