#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ll;
const int N = 2e5+9;
const int B = 131;
int n,ans;
char s1[N],s2[N];
ll h1[N],h2[N],rh1[N],rh2[N],p[N];
ll H1(int l, int r) {return h1[r] - h1[l - 1] * p[r - l + 1];}
ll H2(int l, int r) {return h2[r] - h2[l - 1] * p[r - l + 1];}
ll RH1(int l, int r) {return rh1[l] - rh1[r + 1] * p[r - l + 1];}
ll RH2(int l, int r) {return rh2[l] - rh2[r + 1] * p[r - l + 1];}
int main()
{
	scanf("%d %s %s", &n, s1 + 1, s2 + 1);
	p[0] = 1;
	for (int i = 1; i <= n; ++i)
	{
		h1[i] = h1[i - 1] * B + s1[i];
		h2[i] = h2[i - 1] * B + s2[i];
		p[i] = p[i - 1] * B;
	}
	for (int i = n; i >= 1; --i)
	{
		rh1[i] = rh1[i + 1] * B + s1[i];
		rh2[i] = rh2[i + 1] * B + s2[i];
	}
	for (int i = 1; i <= n; ++i)
	{
		// s1 格子 
		int l = 1,r = min(i - 1, n - i),res = 0;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H1(i - mid, i - 1) == RH1(i + 1, i + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		int pos1 = i - res - 1,pos2 = i + res;
		l = 0,r = min(pos1 - 1, n - pos2),res = -1;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H1(pos1 - mid, pos1) == RH2(pos2, pos2 + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		ans = max(ans, pos2 + res - pos1 + res + 2);
		
		// s2 格子
		l = 1,r = min(i - 1, n - i),res = 0;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H2(i - mid, i - 1) == RH2(i + 1, i + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		pos1 = i - res,pos2 = i + res + 1;
		l = 0,r = min(pos1 - 1, n - pos2),res = -1;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H1(pos1 - mid, pos1) == RH2(pos2, pos2 + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		ans = max(ans, pos2 + res - pos1 + res + 2);
		
		// s1 s2 连接
		l = 0,r = min(i - 1, n - i),res = -1;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H1(i - mid, i) == RH2(i, i + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		ans = max(ans, 2 * res + 2);
		
		if (i == n) continue;
		
		// s1 i~i+1 连接
		l = 0,r = min(i, n - i),res = -1;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H1(i - mid, i) == RH1(i + 1, i + 1 + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		if (res != -1)
		{
			pos1 = i - res - 1,pos2 = i + 1 + res;
			l = 0,r = min(pos1 - 1, n - pos2),res = -1;
			while (l <= r)
			{
				int mid = (l + r) >> 1;
				if (H1(pos1 - mid, pos1) == RH2(pos2, pos2 + mid)) res = mid,l = mid + 1;
				else r = mid - 1;
			}
			ans = max(ans, pos2 + res - pos1 + res + 2);
		}
		
		// s2 i~i+1 连接
		l = 0,r = min(i, n - i),res = -1;
		while (l <= r)
		{
			int mid = (l + r) >> 1;
			if (H2(i - mid, i) == RH2(i + 1, i + 1 + mid)) res = mid,l = mid + 1;
			else r = mid - 1;
		}
		if (res != -1)
		{
			pos1 = i - res,pos2 = i + 2 + res;
			l = 0,r = min(pos1 - 1, n - pos2),res = -1;
			while (l <= r)
			{
				int mid = (l + r) >> 1;
				if (H1(pos1 - mid, pos1) == RH2(pos2, pos2 + mid)) res = mid,l = mid + 1;
				else r = mid - 1;
			}
			ans = max(ans, pos2 + res - pos1 + res + 2);
		}
	}
	printf("%d\n", ans);
	return 0;
}