#include<stdio.h>
#include<string.h>
int main()
{
    char a[5000], b[5000], temp;
    int len, i, t;
    while (scanf("%s%s", a, b) != EOF)
    {
        int c = 0, d = 0, num = 0;
        len = strlen(a);
        for (i = 0; i < len; i++)
        {
            if (a[i] == '+')
                c++;
            if (b[i] == '+')
                d++;
        }
        if (c != d)
        {
            printf("-1\n");
            continue;
        }
        i = 0;
        while (i < len)
        {
            if (a[i] == b[i])
            {
                i++;
                continue;
            }
            else
            {
                t = i;
                temp = a[i];
                while (b[i] != a[t])
                    i++;
                while (i > t)
                {
                    b[i] = b[i-1];
                    i--;
                    num++;
                }
                b[t] = temp;
                i = t + 1;
            }
        }
        printf("%d\n",num);
    }
    return 0;
}