#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
#include <vector>
#pragma GCC target ("avx2")

#include<bits/stdc++.h>
#include<math.h>
using namespace std;

typedef long long int ll;
typedef long double ld;
typedef pair<ll, ll> pl;
typedef vector<ll> vl;
#define FD(i, r, l) for(ll i = r; i > (l); --i)

#define K first
#define V second
#define G(x) ll x; cin >> x;
#define GD(x) ld x; cin >> x;
#define GS(s) string s; cin >> s;
#define EX(x) { cout << x << '\n'; exit(0); }
#define A(a) (a).begin(), (a).end()
#define F(i, l, r) for (ll i = l; i < (r); ++i)

template<typename A, typename B>
A& chmax(A &a, B b) { return a < b ? (a=b): a; }

template<typename A, typename B>
A& chmin(A &a, B b) { return a > b ? (a=b): a; }




const ll N = 1;
const ll M = 1000000007; // 998244353


int main(){
//    freopen("a.in", "r", stdin);
//    freopen("a.out", "w", stdout);

    ios_base::sync_with_stdio(false); cin.tie(0);
    cout << fixed << setprecision(20);

    G(n) G(k)
    ll thresh = n * n - n;
    if (n == 2) {
        if (k == 0) cout << "YES\n..\n..\n";
        else if (k == 1) cout << "YES\n..\n.#\n";
        else cout << "NO\n";
        exit(0);
    }
    
    if (k > thresh) {
        cout << "NO\n";
    }     else {
        cout << "YES\n";
        F(i, 0, n) {
            F(j, 0, n) {
                bool ok = true;
                if (n % 2 == 0) {
                    if (i == n/2 and j == n/2 - 1) ok = false;
                    else if (i == n/2 - 1 and j == n/2) ok = false;
                    else if (i == n/2 - 1 and j == n/2 - 1) ok = true;
                    else if (i == n/2 and j == n/2) ok = true;
                    else ok &= i != j;
                } else {
                    ok &= i != j;
                }
                ok &= k > 0;
                if (ok) {
                    k--; cout << "#";
                } else cout << ".";
            }
            cout << '\n';
        }
    }
}