Run Time Error in a C++ code

I am getting Run-Time-Error in a C++ code. I am giving my source code. Need Help! Thanks in advance.

Source code:

#include <map>
#include <cstdio>
using namespace std;

class Pair{
    public:
    int x;
    int y;
};

map < Pair , int > mapper;

int main(){
    Pair a;
    a.x = 8;
    a.y = 9;
    mapper[a] = 1; // Here i get Run-Time-Error
    return 0;
}