H,W=map(int,input().split())
S=[input() for h in range(H)]
ans="NO"
cnt=0
for h in range(H):
    for w in range(W):
        if S[h][w]==".":
            cnt+=1
for _ in range(4):
    for h in range(H-1):
        for w in range(W-1):
            lh,rw=h,w+1
            while lh and S[lh-1][w]==".":
                lh-=1
            while rw<W and S[lh][rw]==".":
                rw+=1
            lw,rh=w,h+1
            while lw and S[h][lw-1]==".":
                lw-=1
            while rh<H and S[rh][lw]==".":
                rh+=1
            if any(S[i][rw-1]=="#" for i in range(lh,rh)):
                continue
            if any(S[rh-1][i]=="#" for i in range(lw,rw)):
                continue
            if ((rh-lh)+(rw-lw)-2)*2==cnt and rh-lh>=2 and rw-lw>=2:
                ans="YES"
    S=[[S[h][W-1-w] for h in range(H)] for w in range(W)]
    H,W=W,H
print(ans)