#define M 4
int E=-1,a[M],b;
int c(int n){return b>=M?E:(a[b++]=n);}
int d(void){return b<=0?E:a[--b];}

int main(void)
{
  printf("push:%d\n", c(1));
  printf("push:%d\n", c(2));
  printf("push:%d\n", c(3));
  printf("push:%d\n", c(4));
  printf("push:%d\n", c(5));

  printf("pop :%d\n", d());
  printf("pop :%d\n", d());
  printf("pop :%d\n", d());
  printf("pop :%d\n", d());
  printf("pop :%d\n", d());
  return 0;
}

push:1
push:2
push:3
push:4
push:-1
pop :4
pop :3
pop :2
pop :1
pop :-1