check_format(list l)
{
    integer i;
    text s;

    if (~l != 49) {
        error("bad field count");
    }

    s = l[0];
    if (match("????-??-??", s)) {
        error("bad date format");
    }
    l[0] = s.delete(7).delete(4).atoi;

    i = 1;
    while (i < 49) {
        atof(l[i]);
        i += 1;
        l[i >> 1] = atoi(l[i]);
        i += 1;
    }

    l.erase(25, -1);
}

main(void)
{
    integer goods, i, v;
    file f;
    list l;
    index x;

    goods = 0;

    f.affix("readings.txt");

    while (f.list(l, 0) != -1) {
        if (!trap(check_format, l)) {
            if ((x[v = lf_x_integer(l)] += 1) != 1) {
                v_form("duplicate ~ line\n", v);
            }

            i = 1;
            l.ucall(min_i, 1, i);
            goods += iclip(0, i, 1);
        }
    }

    o_(goods, " good lines\n");

    0;
}