List* createList(){
    FILE *fp;
    if((fp=fopen("input.bin","rb"))==NULL)exit(1);
     List* root=NULL;
    while(1){
        List* curr=(List*)malloc(sizeof(item));

        if(fread(curr,sizeof(item),1,fp)!=1)break;
        curr->next=root;
        root=curr;
    }
    return root;

}