/*
* Funcao que remove o ultimo frame da pilha, liberando o espaco
*
*/
void dropFrame(){
unsigned int *local;
struct snode * p;
if(topo==NULL)
erroFatal("Stack is empty");
while(topo!=NULL&&topo!=base){
pop();
}
checa(topo);
p = topo->prox;
unsigned int valor = topo->valor;
//free(topo);
topo=p;
checa(topo);
local=(unsigned int *)valor;
//free(local);
p = topo->prox;
valor = topo->valor;
//free(topo);
topo=p;
base=(struct snode *)valor;
//printf("local=0x%X\n",(unsigned int)local);
//printf("base=0x%X\n",(unsigned int)base);
}
int main() {
while(1) {
scanf("%d", &n); if(!n) break;
for(int i=0; i<n; i++) {
scanf("%s", matriz[i]);
}
int cont = 0;
memset(visi, false, sizeof(visi));
for(int i=0; i<n; i++) if(!visi[i]) {
cont++;
for(int j=0; j<n; j++) if(matriz[i][j] == '1') {
if(!checa(j, i)) {
cont = -1;
}
visi[j] = true;
}
visi[i] = true;
if(cont == -1) break;
}
if(cont == -1) {
printf("impossivel\n");
} else {
printf("%d\n", cont);
}
}
}
void push(unsigned int valor, char tipo){
struct snode *novo = calloc(1,sizeof(struct snode));
checa(novo);
novo->valor=valor;
novo->tipo=tipo;
novo->prox=topo;
topo=novo;
}
void newFrame(unsigned int lv_size){
unsigned int * local = calloc(lv_size+1, sizeof(unsigned int));
checa(local);
local[0]=lv_size;
push((unsigned int) base,0);
push((unsigned int) local,0);
//printf("local=0x%X\n",(unsigned int)local);
//printf("base=0x%X\n",(unsigned int)base);
base=topo;
}
void setLocalVar(int index, int value){
if(base==NULL){
erroFatal("Stack frame is empty");
}
unsigned int * local = (unsigned int *) base->valor;
checa(local);
if(index<0 || index >= local[0]){
erroFatal("Access out of bounds");
}
local[index+1]=value;
}