#include<bits/stdc++.h>
using namespace std;
map<string,int>a;
int main()
{
    string n,m;
    cin >> n >> m;
    if(n == m)
    {
        cout << 0;return 0;
    }
    int num = 0;
    while(a[n] == 0)
    {
        num++;
        a[n]++;
        for(int i = 0;i<n.size();i++)
        {
            if(n[i] == 'z')
            {
                n[i] = 'a';
            }
            else if(n[i] == '9')
            {
                n[i] = '0';
            }
            else
            {
                n[i]++;
            }
        }
        if(n == m)
        {
            cout << num;
            return 0;
        }
    }
    cout << "IMPOSSIBLE";
    return 0;
}