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

#define ll long long
const int N = 1e6 + 10;

string s1, s2;
ll vt[N];
ll sum;


/*

.#.#.#...
.##.....#


.##.##
......
*/


signed main() {
    cin >> s1 >> s2;
    for (int i = 0; i < (ll)s1.size(); i++) {
        if (s1[i] == '#') {
            vt[i] = vt[i] + 1;
            sum++;
        }
        if (s2[i] == '#') {
            vt[i] = vt[i] + 2;
            sum++;
        }
//      cout << vt[i] << " ";
    }
//  cout << endl;
    ll ops = 0;
    for (int i = 0; i < (ll) s1.size(); i++) {
        if (vt[i] != 0) {
            ops = i;
            break;
        }
    }
//  cout << ops << endl;
    ll sm = 0;
    ll dan = -1;
    ll disdan = -1;
    ll dbl = -1;
    ll disdbl = -1;
    ll ans = 0;
    for (ll i = ops; i < (ll) s1.size(), sm < sum; i++) {
        if (vt[i] == 1) {
            sm++;
            if (dan != -1) {
                if (dan == 1) {
                    ans += (i - disdan - 1);
                    dan = 1;
                    disdan = i;
                    continue;
                } else if (dan == 2) {
                    ans += (i - disdan);
                    dbl = 1;
                    dan = -1;
                    disdbl = i;
                    continue;
                }
//              cout << ans << " sm" << sm << endl;
            } else if (dbl != -1) {
                ans += (i - disdbl - 1);
                dbl = -1;
                dan = 1;
                disdan = i;
                continue;
            }
            dan = 1;
            disdan = i;
//          dan = 1;
//          disdan = i;
        } else if (vt[i] == 2) {
            sm++;
            if (dan != -1) {
                if (dan == 2) {
                    ans += (i - disdan - 1);
                    dan = 2;
                    disdan = i;
                } else if (dan == 1) {
                    ans += (i - disdan);
                    dan = -1;
                    dbl = 1;
                    disdbl = i;
                }
                continue;
            } else if (dbl != -1) {
                ans += (i - disdbl - 1);
                dbl = -1;
                dan = 2;
                disdan = i;
                continue;
            }
            dan = 2;
            disdan = i;
//          dan = 2;
//          disdan = i;
        } else if (vt[i] == 3) {
            sm += 2;
            if (dan != -1) {
                ans += (i - disdan - 1);
                dan = -1;
            } else if (dbl != -1) {
                ans += (i - disdbl - 1);
            }
            dbl = 1;
            disdbl = i;
        }
    }

    cout << ans << endl;
    return 0;
}
/*

..#...
.....#


..###.
.....#

..####
.....#


#..#.#
#...#.

*/