Sorting on pair of vector with first element doesnt work C++

I'm trying to solve a question : QUESTION

So in order to solve it I must sort the pair of vector but when I try'a do it,It doesn't work, So how to fix it? MY Code

#include <iostream>
#include <vector>
using namespace std;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie();
    cout.tie();
    #ifndef ONLINE_JUDGE
        freopen("input.txt","r",stdin);
        freopen("output.txt","w",stdout);
    #endif
    int TestCase;
    cin>>TestCase;
    while(TestCase--){
        int HardDisk,Total;
        vector<pair<int,int>>Data;
        cin>>Total>>HardDisk;
        while(Total--){
            int IMDB,Size;
            cin>>Size>>IMDB;
            Data.push_back(make_pair(Size,IMDB));
        }
        sort(Data.begin(),Data.end());
        for(int i=0;i<Data.size();i++){
            cout<<Data[i].first<<" "<<Data[i].second<<endl;
        }
    }
}

from Recent Questions - Stack Overflow https://ift.tt/3d9yxHW
https://ift.tt/eA8V8J