implementation of pushback function in c++

#include <iostream>
#include <string>

using namespace std;

int main()
{
string s1 , s2 ;
cin>>s1;

int i;

for(i=s1.size()-1 ; i>=0 ; i--)
{
     s2.push_back(s1[i]);
}

cout << s2;

return 0;

}