from heapq import heappop,heappush 

n=int(input())
s=input()
y='yuki'
h=[]
ans=0

for i in s:
    heappush(h,-ord(i))

f=1
while len(h) > 0 and f == 1:
    f=0
    for i in range(4):
        if len(h) == 0:
            break
        t = heappop(h)
        if -t > ord(y[i]):
            f=1
            ans += 1
            break
            
print(ans)