push(x, y); while(true) { x = popx(); if (x ==-1) return true; y = popy();
push(x, y); while(true) { x = popx(); if (x ==-1) return true; y = popy();
push(x, y); while(true) { x = popx(); if (x ==-1) return; y = popy();
push(x, y); while(true) { x = popx(); if (x ==-1) return; y = popy();
push(x, y); while(true) { x = popx(); if (x==-1) return true; y = popy();
push(x, y); while(true) { x = popx(); if (x==-1) return true; y = popy();