Understanding getline c++

string s = "HackerRank ";
string s2;
getline(cin, s2);
s+=s2;
cout<<s;

for input:

is the best place to learn and practice coding!

it is giving output:

HackerRank the best place to learn and practice coding!

Can someone pleasee help me understand why it is giving this problem?

It is however working with:

string s = "HackerRank ";
string s2,ws;
cin>>ws;
getline(cin, s2);
s+=ws;
s+=s2;
cout<<s;

It is giving the expected output:

HackerRank is the best place to learn and practice coding!

for the same input