#include<iostream>
#include<string>
#include<cmath>
#include<queue>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<functional>
#include<algorithm>
#include<cstdio>
#include<random>
#include<unordered_map>
using namespace std;
//---------------------------------------------------
//ライブラリゾーン！！！！
#define int long long
#define str string
#define rep(i,j) for(int i=0;i<(int)(j);i++)
typedef long long ll;
typedef long double ld;
const ll inf = 4523372036854775807;
const ll Mod=1000000007;
short gh[2][4] = { {0,0,-1,1},{-1,1,0,0} };
struct P {
ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B {//隣接リスト表現
ll to, cost;
};
struct S {//辺の情報を入れる変数
int from, to, cost;
};
struct H {
int x, y;
};
bool operator<(H a, H b) {
if (a.x != b.x) return a.x < b.x;
return a.y < b.y;
}
ll gcm(ll i, ll j) {//最大公約数
if (i > j) swap(i, j);
if (i == 0) return j;
return gcm(j%i, i);
}
ld rad(ld a, ld b, ld c, ld d) {
return sqrt(pow(a - c, 2) + pow(b - d, 2));
}//rad＝座標上の2点間の距離
int ari(int a, int b, int c) {
return (a + b)*c / 2;
}//等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
if (b <= c || d <= a) return 0;
return 1;
}//[a,b),[c,d)
ll mod_pow(ll x,ll n,ll p){
    ll res=1;
    while(n>0){
        if(n&1) res=res*x%p;
        x=x*x%p;
        n>>=1;
    }
    return res;
}
//---------------------------------------------------
//+++++++++++++++++++++++++++++++++++++++++++++++++++
int n,m,ans;
string s1,s2;
int dp[2001][2001][2];
int solve(int x,int y,int z){
	if(x==n&&y==m){
		if(z==0) return -inf;
		return 0;
	}
	if(dp[x][y][z]>0){
		return dp[x][y][z];
	}
	int sum=0;
	if(x<n){
		if(s1[x]=='O'&&z==1){
			sum=max(sum,solve(x+1,y,0)+1);
		}
		if(s1[x]=='I'&&z==0){
			sum=max(sum,solve(x+1,y,1)+1);
		}
	}
	if(y<m){
		if(s2[y]=='O'&&z==1){
			sum=max(sum,solve(x,y+1,0)+1);
		}
		if(s2[y]=='I'&&z==0){
			sum=max(sum,solve(x,y+1,1)+1);
		}
	}
	if(z==0&&sum==0){
		sum=-inf;
	}
	ans=max(ans,sum);
	return dp[x][y][z]=sum;
}
signed main() {
    cin>>n>>m;
    cin>>s1>>s2;
    for(int i=0;i<=n;i++){
		for(int j=0;j<=m;j++){		
			solve(i,j,0);
		}
	}
    cout<<ans<<endl;
    getchar(); getchar();
}

