C++ substr() function not working properly.

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string

C++14

#include <iostream>
#include<string> 

using namespace std;

int main()
{

string s = "abaxyzzyxf" ; 

cout<< s.substr(5,6) ; 

    

    return 0;
}

The above code prints zzyxf and not zz.

What I have tried:

I was writing code to find longest palindrome substring in the given string s and while debugging I came to know that my substr() function is not working properly.

It prints zzyxf and not zz.

Why does this happen ?