HAProxy stands for High Availability Proxy, If you are running the Ubuntu Xenial-16.04 LTS operating system and install  HAProxy-1.5-stable version

first, need to enable a Dedicated PPA using below commands on Ubuntu Xenial-16.04 LTS

# apt-get install software-properties-common

# add-apt-repository ppa:vbernat/haproxy-1.5

Execute the below commands,

# apt-get update

# apt-get install haproxy

Now, able to access the  latest release of HAProxy-1.5-stable