//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("avx")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define re return
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define sqrt(x) sqrt(abs(x))
#define mp make_pair
#define pi (3.14159265358979323846264338327950288419716939937510)
#define fo(i, n) for(int i = 0; i < n; ++i)
#define ro(i, n) for(int i = n - 1; i >= 0; --i)
#define unique(v) v.resize(unique(all(v)) - v.begin())
template <class T> T abs (T x) { re x > 0 ? x : -x; }
template <class T> T sqr (T x) { re x * x; }
template <class T> T gcd (T a, T b) { re a ? gcd (b % a, a) : b; }
template <class T> int sgn (T x) { re x > 0 ? 1 : (x < 0 ? -1 : 0); }
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<string> vs;
typedef double D;
typedef long double ld;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
typedef unsigned long long ull;
typedef tree <pair<int, char>, null_type, less<pair<int, char>>, rb_tree_tag, tree_order_statistics_node_update> _tree;
string str1, str2;
int main() {
cin >> str1 >> str2;
reverse(all(str1));
reverse(all(str2));
int ans = 0;
while (!str1.empty() || !str2.empty()) {
if (!str1.empty() && !str2.empty()) {
char b1 = str1.back();
char b2 = str2.back();
if (b1 == b2 && b2 == 'L') str1.erase(str1.size() - 1, 1), str2.erase(str2.size() - 1, 1);
else if (b1 == 'L') str2.erase(str2.size() - 1, 1);
else if (b2 == 'L') str1.erase(str1.size() - 1, 1);
else str1.erase(str1.size() - 1, 1), str2.erase(str2.size() -1, 1);
} else if (str1.empty()) str2.erase(str2.size() - 1, 1);
else str1.erase(str1.size() - 1, 1);
++ans;
//cout << str1 << ' ' <<str2 << ' ' << ans << endl;
}
cout << ans << endl;
}
