List* createList(){
    FILE *fp;
    if(fp=fopen("input.bin","rb")==0)exit(1);
     List* root=NULL;
    while(1){
        List* curr=(List*)malloc(sizeof(item));

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

}