#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,k; cin >> n >> k;
    int mx=n*n-n;
    if(n==2 and k==2){
        printf("NO\n");
    }
    else if(k>mx and k>0){
        printf("NO\n");
    }
    else{
        printf("YES\n");
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                if((i==j and(n%2 or (0<i and i+1<n))) or k==0 or (i==0 and j+1==n and n%2==0) or (i==n-1 and j==0 and n%2==0))printf(".");
                else{
                    printf("#");
                    k--;
                }
            }
            printf("\n");
        }
    }
}