"""
[24076: IOI 文字列 (IOI String)](https://www.acmicpc.net/problem/24076)
Tier: Bronze 2
Category: 구현
"""
def solution(s):
return sum([1 if s[i] != "IO"[i % 2] else 0 for i in range(len(s))])
if __name__ == '__main__':
input()
print(solution(input()))