#include<bits/stdc++.h>
#define int long long
using namespace std;
string s,t;
signed main(){
    cin>>s>>t;
    if(s==t){
        cout<<0;
        return 0;
    }
    for(int j=1;j<=300;j++){
        for(int i=0;i<s.size();i++){
            if(s[i]=='9') s[i]='0';
            else if(s[i]>='0' and s[i]<='9') s[i]=s[i]+1;
            if(s[i]=='z') s[i]='a';
            else if(s[i]>='a' and s[i]<='z')s[i]=s[i]+1;
        }
		if(s==t){
            cout<<j;
            return 0;
        }
    }
    cout<<"IMPOSSIBLE";
    return 0;
}