#include <vector>
#include <iostream>
using namespace std;
char nxt(char c) {
    if(c=='Q') return 'U';
    return c;
}
int main() {
    vector<vector<string>> cost(3);
    for(int i : {0,1,1,1,1,2}) {
        string t; cin >> t;
        cost[i].push_back(t);
    }
    const int n = 16;
    string dp(n*2+1,'Z'+1);
    dp[0]='A';
    for(int i=0;i<n;++i) {
        string ndp(n*2+1,'Z'+1);
        for(int j=0;j<=2;++j) {
            for(auto& s : cost[j]) {
                for(int x=0;x<=n*2;++x) if(dp[x]<=s[i]) {
                    ndp[x+j]=min(ndp[x+j],nxt(s[i]));
                }
            }
        }
        swap(dp,ndp);
    }
    int ans=0;
    while(ans<=n*2 and dp[ans]>'Z') ++ ans;
    if(ans>n*2) cout << "impossible\n";
    else cout << ans << '\n';
}