// Problem: 搭乘 IOI 火车
// Contest: Virtual Judge - LibreOJ
// URL: https://vjudge.net/problem/LibreOJ-2762#author=GPT_vi
// Memory Limit: 256 MB
// Time Limit: 1000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

# include <bits/stdc++.h>
using namespace std;
#define int long long

int n,m,res,a[2005],b[2005],dp[2005][2005][2];
string s,t;
signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin >> n >> m;
	cin >> s >> t;
	s = '#' + s;
	t = '#' + t;
	for (int i = 1; i <= n; i++)
	{
		a[i] = (s[i]=='O');
	}
	for (int i = 1; i <= m; i++)
	{
		b[i] =(t[i]=='O');
	}
	for (int i = 0; i <= n; i++) for (int j = 0; j <= m; j++) dp[i][j][1]=-1e9;
	for (int i = 0; i <= n; i++)
	{
		for (int j = 0; j <= m; j++)
		{
			// dp[i][j][k] la bat dau o vi tri i trong xau s 
			// va vi tri j trong xau t va ky tu tiep theo can la k
			if (i<n)
			{
				dp[i+1][j][1-a[i+1]] = max(dp[i+1][j][1-a[i+1]],dp[i][j][a[i+1]]+1);
			}
			if (j < m)
			{
				dp[i][j+1][1-b[j+1]] = max(dp[i][j+1][1-b[j+1]],dp[i][j][b[j+1]]+1);
			}
		}
	}
	for (int i = 0; i <= n; i++)
	{
		for (int j = 0; j <= m; j++)
		{
			res = max(res,dp[i][j][1]);
		}
	}
	cout <<res;
}