Matrix multiplication

const int MAXN = 801;

bitset<MAXN> r1[MAXN], r2[MAXN], c1[MAXN], c2[MAXN];

int a[MAXN][MAXN];

int main()
{
    int n;
    while (~RI(n))
    {
        REP(i, n) REP(j, n)
        {
            RI(a[i][j]);
            if (a[i][j] >= 3)
                a[i][j] %= 3;
            r1[i][j] = a[i][j] >> 1;
            r2[i][j] = a[i][j] & 1;
        }
        REP(i, n) REP(j, n)
        {
            RI(a[i][j]);
            if (a[i][j] >= 3)
                a[i][j] %= 3;
            c1[j][i] = a[i][j] >> 1;
            c2[j][i] = a[i][j] & 1;
        }
        REP(i, n) REP(j, n)
        {
            a[i][j] = (r1[i] & c1[j]).count() ;
            a[i][j] += ((r1[i] & c2[j]).count()) << 1;
            a[i][j] += ((r2[i] & c1[j]).count()) << 1;
            a[i][j] += (r2[i] & c2[j]).count() ;
            if (a[i][j] >= 3)
                a[i][j] %= 3;
        }
        REP(i, n) REP(j, n)
            printf("%d%c", a[i][j], j == n - 1 ? '\n' : ' ');
    }
    return 0;
}