char *read_str(){
        int c, i = 0;
        char *s = (char *)malloc(0 * sizeof(char));
        while ((c = getchar()) != '\n'){
            s = (char *)realloc(s, (i + 1) * sizeof(char));
            s[i] = (char)c;
            ++i;
        }
        s = (char *)realloc(s, i  * sizeof(char));
        s[i] = '\0';
        return s;
    }