Controlling cout in a for loop

Here is my code:

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main()
{

stringstream os; // Initialize stringstream "os"
string mValue = "month"; // Initialize mValue "month"
int iValue = 1; // Initialize iValue "1"

for(int iValue = 1; iValue < 13; ++iValue) // Iteration 1: 1 < 12 so execute the following:
{
    os << mValue << "" << iValue; // Glue mValue and iValue together
    cout << os.str() << endl; // Print glued mValue and iValue
}

return 0;

}

This results in the following output:

month1
month2month2
month3month3month3
month4month4month4month4
month5month5month5month5month5
month6month6month6month6month6month6
month7month7month7month7month7month7month7
month8month8month8month8month8month8month8month8
month9month9month9month9month9month9month9month9month9
month10month10month10month10month10month10month10month10month10
month11month11month11month11month11month11month11month11month11month11
month12month12month12month12month12month12month12month12month12month12month12

The desired output is:

month1
month2
month3
month4
month5
month6
month7
month8
month9
month10
month11
month12

Being a noob at coding, I understand why this is happening but I don't know how to fix it. I tried to place cout outside of the for loop but that results in

month1month2month3month4month5month6month7month8month9month10month11month12

I'm out of ideas and I hope you can tell me how to get this right.