D = int(input())
S = "x" * D + input().rstrip() + input().rstrip() + "x" * D
x, y = [], []
cntX, cntO = 0, 0
for i in range(len(S)):
    if S[i] == "x":
        if i != 0 and S[i - 1] == "o":
            x.append(cntO)
            cntO = 0
        cntX += 1
    else:
        if i == 0 or S[i - 1] == "x":
            y.append(cntX)
            cntX = 0
        cntO += 1
if cntO > 0:
    x.append(cntO)
y.append(cntX)
#print(x, y)
if len(x) == 0:
    print(D)
    exit()
MAX = 0
for i in range(len(y)):
    if y[i] <= D:
        if i == 0:
            MAX = max(MAX, y[i] + x[i])
        elif i == len(y) - 1:
            MAX = max(MAX, x[i - 1] + y[i])
        else:
            MAX = max(MAX, x[i - 1] + y[i] + x[i])
    else:
        if i == 0:
            MAX = max(MAX, D + x[i])
        elif i == len(y) - 1:
            MAX = max(MAX, x[i - 1] + D)
        else:
            MAX = max(MAX, x[i - 1] + D)
            MAX = max(MAX, D + x[i])
print(MAX)