How to Subtract the first element in a vector from another first element in another vector?

I have 2 vectors of ints.

say the first one has (2,1). and the second one (1,1).

I am trying to subtract numbers like this:

2 1 - 1 1 = 1 0

then I need to add these 2 numbers so the final answer would be 1.

I've tried a for loop, but it's subtracting each number from each element, instead of only the first one.

This is what I've tried so far.

vector<int> temp;

for(unsigned i =0; i < Vec1.size(); i++)
 for(unsigned o =0; o < Vec2.size(); o++)
   temp.push_back(Vec1.at(i).nums- Vec2.at(o).nums);

//where nums, are just the numbers showed above

The output as you would expect is : 1 1 0 0

and I need it to be:

1 0

then I can just do a for loop to add all the ints together.

Any help, would be greatly appreciated!