D=int(input())
S=input();S+=input()
S=[1 if s=="o" else 0 for s in S]
S=[0]*14+S+[0]*14

X=0
for i in range(42-D+1):
    T=S.copy()
    F=1
    for j in range(D):
        if S[i+j]==0:
            T[i+j]=1
        else:
            F=0

    if not F:
        continue

    U=[0]*43
    for x in range(42):
        if T[x]==1:
            U[x+1]=U[x]+1
    X=max(X,max(U))
print(X)