std::sort in C++ not working

I am trying to sort a vector of integers using std::sort. I'm quite new to C++ so there might be a basic error. This is my header file so far:

class MaximumGates {

    private:
        int maxGates;

    public:
        int maximumGates(const vector<int> &arrivesIn, const vector<int> &departsIn);

};

int maximumGates(const vector<int> &arrivesIn, const vector<int> &departsIn){
    int maxDeparture = *std::max_element(departsIn.begin(), departsIn.end());
    sort(departsIn.begin(), departsIn.end());

    return maxDeparture;
}

It is accessed in the main() method as such:

#include "MaximumGates.h"

#include <iostream>
using std::cout;
using std::endl;

#include <vector>
using std::vector;

    int main() {
        int retval = 0;

        {
            vector<int> arrives{360, 400, 700};
            vector<int> departs{900, 515, 780};

            int maxGates = maximumGates(arrives,departs);

            ...

Upon compiling, there are 20+ errors e.g.

/Applications/http://ift.tt/2y3mIxU: note: 
      candidate template ignored: could not match 'shared_ptr<type-parameter-0-0>' against
      'const int'
swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT
^
/Applications/http://ift.tt/2hTDo71: note: 
      candidate template ignored: could not match 'weak_ptr<type-parameter-0-0>' against
      'const int'
swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT
^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.