from collections import defaultdict
from functools import reduce
from numpy import roll


def main():
    N = int(input())
    S = input()
    CON = "con"

    buff = [defaultdict(lambda: 0) for _ in range(3)]

    for i, j in enumerate(S):
        buff[i%3][j] += 1
    
    cnt = [reduce(min,
                  map(lambda x, y: x[y],
                      roll(buff, i), CON))
           for i in range(3)]

    if cnt == N:
        print(N)
    else:
        print(min(sum(cnt), N-1))

if __name__ == '__main__':
    main()