// Ivan Carvalho

// Solution to https://www.beecrowd.com.br/judge/problems/view/1063

#include <cstdio>

#define MAX 30

int n, tam;

char saida[MAX], pilha[MAX], entrada[MAX];

void pop() {

if (tam > 0) tam--;

}

void push(char x) { pilha[++tam] = x; }

void clear() { tam = 0; }

char top() { return pilha[tam]; }

int main() {

while (scanf("%d", &n) && n != 0) {

clear();

for (int i = 1; i <= n; i++) scanf(" %c", &entrada[i]);

for (int i = 1; i <= n; i++) scanf(" %c", &saida[i]);

int j = 1;

push(entrada[j++]);

printf("I");

for (int i = 1; i <= n; i++) {

while (top() != saida[i] && j <= n) {

printf("I");

push(entrada[j++]);

}

if (top() == saida[i]) {

printf("R");

pop();

} else {

printf(" Impossible");

break;

}

}

printf("\n");

}

return 0;

}