[백준] No.5525 IOIOI 完

# ---------- Import ----------
import sys
input = sys.stdin.readline

# ---------- Main ----------
N = int(input())
S_length = int(input()) + 1
S = list(input().rstrip()); S += S[-1]

START = S[0]
Pn_length, result = 1, 0

for i in range(1, S_length):
    if S[i-1] != S[i]:
        Pn_length += 1
        
    else:
        END = S[i-1]
        
        # Calculating
        O_count = (START, END).count("O")
        Pn_length -= O_count
        
        Pn_length = (Pn_length + 1) // 2
        if Pn_length > N: result += Pn_length - N 
        
        START = S[i]
        Pn_length = 1
        
print(result)