#include <bits/stdc++.h>
//#include <windows.h>
//#include <psapi.h>
//#include <time.h>
using namespace std;
#define debug(x) std::cerr<<#x<<'='<<x<<std::endl
signed main()
{
	//  freopen("Luogu_P_1877.cpp.in","r",stdin);
	//  freopen("Luogu_P_1877.cpp.out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	string s, t;
	//  clock_t start,end;    //定义clock_t变量
	//  start = clock();      //开始时间
	cin >> s >> t;
	//  end = clock();   //结束时间
	//  cout<<"time = "<<double(end-start)/CLOCKS_PER_SEC<<"s"<<endl;//输出时间
    if (s.size() != t.size()) {
		cout << "IMPOSSIBLE";
		return 0;
	}
	if (s == t) {
		cout << 0;
		return 0;
	}
//	int cnt = -1;
//	int cntnum = -1;
	for (int i = 1; i <= 265; i++) {
		for (int j = 0; j < s.size(); j++) {
			if (s[j] >= '0' and s[j] <= '9') {
				if (s[j] == '9') s[j] = '0';
				else s[j] = s[j] + 1;
			}
			if (s[j] >= 'a' and s[j] <= 'z') {
				if (s[j] == 'z') s[j] = 'a';
				else s[j] = s[j] + 1;
			}
		}
		if (s == t) {
			cout << i;
			return 0;
		}
	}
	//  HANDLE hd = GetCurrentProcess();
	//  PROCESS_MEMORY_COUNTERS pmc;
	//  GetProcessMemoryInfo(hd, &pmc, sizeof(pmc));
	//  printf("%lf", double(pmc.WorkingSetSize) / 1024 / 1024);//单位MiB
	cout << "IMPOSSIBLE";
	//  fclose(stdin);
	//  fclose(stdout);
	return 0;
}