What will be the output of the following C++ code?

#include <iostream>
#include <deque>
using namespace std;
int main ()
{
    deque<int> mydeque;
    int sum (0);
    mydeque.push_back ( 10 );
    mydeque.push_back ( 20 );
    mydeque.push_back ( 30 );
    while (!mydeque.empty())
    {
        sum += mydeque.back();
        mydeque.pop_back();
    }
    cout << sum << '\n';
    return 0;
}