def DocTep():
fi=open("DaySo.inp",'r')
n=int(fi.readline())
a =str(fi.readline())
fi.close()
return n,a
def XuLi(n,a):
if not a:
return 0
l = [1] * n
for i in range (1 , n):
for j in range(i):
if a[i] > a[j] and l[i]< l[j] + 1 :
l[i] = l[j]+1
maximum = max(l)
return maximum
def GhiTep(m):
fo=open("DaySo.out",'w')
print(m,file=fo)
fo.close()
n,a=DocTep()
m=XuLi(n,a)
GhiTep(m)