• Since there are n astronauts ,there are N choose 2 pairs. Initialise the answer to this number.
• But we aren't allowed astronaut pairs from the same country.
• So subtract the astronaut pairs from same country from the total answer.
• Do this for every country which has more than 1 astronaut.

long int ans= (n*(n-1))/2;

for(auto it = m.begin(); it!= m.end(); it++){
    long int astros = it->second;
     if(astros > 1)
        ans-= (astros*(astros-1))/2; 
}
return ans;