//本题实质为：判断I是否是P的子序列

#include <iostream>
#include <cstring>

using namespace std;

const int N = 100010;

char a[N],b[N];

int main(){

    int T;
    cin >> T;
    for(int cases = 1;cases <= T;cases++){
        cin >> a >> b;
        int n = strlen(a),m = strlen(b);
        int i,j;
        for(i=0,j=0;j<m;j++){
            if(a[i] == b[j]){
                i++;
            }
            if(i == n){
                break;
            }
        }
        if(i == n){
            printf("Case #%d: ",cases);
            cout << m-n << endl;
        }else{
            printf("Case #%d: IMPOSSIBLE",cases);
            cout << endl;
        }
    }

    return 0;
}