import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.stdio;
import std.string;
import std.range;

int readint() {
    return readln.chomp.to!int;
}

int[] readints() {
    return readln.split.map!(to!int).array;
}

int calc(int d, string s) {
    // 平日=0, 休日=1
    int[] ss = s.map!(e => e == 'x' ? 0 : 1).array;

    auto as = 0.repeat().take(d).array;
    auto xs = as ~ ss ~ as; // 2 週間の前後を挟む

    int ans = 0;
    for (int i = 0; i <= xs.length - d; i++) { // i 日目から連続で d 日休暇
        auto ys = xs.dup;

        for (int j = i; j < i + d; j++) { // i 日目から d 日休暇
            if (ys[j] == 1) // 休日はまたがない
                break;
            ys[j] = 1;
        }

        int holidays = 0;
        for (int j = 0; j < xs.length; j++) {
            if (ys[j] == 1) {
                holidays++;
                ans = max(ans, holidays);
            }
            else {
                holidays = 0;
            }
        }
    }
    return ans;
}

void main() {
    int d = readint();
    auto s = readln.chomp;
    auto t = readln.chomp;
    writeln(calc(d, s ~ t));
}