Getting Permission denied (publickey) tyring to connect using ssh

HI,
I am using the following command to connect to a host_ip :
ssh username@host_ip
My username n public key has been added to the server.
The host_ip also appears in known_hosts file .

Files under my .ssh directory :
github_rsa      github_rsa.pub      id_rsa            id_rsa.pub      known_hosts

I tried the ssh command with -v option following was the output :

ssh -v username@host_ip
OpenSSH_6.2p2, OSSLShim 0.9.8r 8 Dec 2011
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: /etc/ssh_config line 102: Applying options for *
debug1: Connecting to host_ip [host_ip] port 22.
debug1: Connection established.
debug1: identity file /Users/robinsuri/.ssh/id_rsa type 1
debug1: identity file /Users/robinsuri/.ssh/id_rsa-cert type -1
debug1: identity file /Users/robinsuri/.ssh/id_dsa type -1
debug1: identity file /Users/robinsuri/.ssh/id_dsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
debug1: Remote protocol version 2.0, remote software version libssh-0.7.0
debug1: no match: libssh-0.7.0
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha1 none
debug1: kex: client->server aes128-ctr hmac-sha1 none
debug1: sending SSH2_MSG_KEXDH_INIT
debug1: expecting SSH2_MSG_KEXDH_REPLY
debug1: Server host key: RSA 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
debug1: Host 'host_ip' is known and matches the RSA host key.
debug1: Found key in /Users/robinsuri/.ssh/known_hosts:2
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/robinsuri/.ssh/id_rsa
debug1: Authentications that can continue: publickey
debug1: Trying private key: /Users/robinsuri/.ssh/id_dsa
debug1: No more authentication methods to try.
Permission denied (publickey).

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I also tried adding the line ChallengeResponseAuthentication yes
  in sshd_config file but still getting the same error. I saw this in one of the solution so thought probably this will make it work. but it didnt.

what could be wrong?

Please help
Thanks