JOI2010春Day1-sengoku.cpp

#include <bits/stdc++.h>
using namespace std;

#define times(n, i) uptil(0, n, i)
#define upto(f, t, i) for(auto _##i = (t), i = decltype(_##i)(f); i <= _##i; i++)
#define uptil(f, t, i) for(auto _##i = (t), i = decltype(_##i)(f); i < _##i; i++)
#define downto(f, t, i) for(auto _##i = (t), i = decltype(_##i)(f); i >= _##i; i--)
#define downtil(f, t, i) for(auto _##i = (t), i = decltype(_##i)(f); i > _##i; i--)
#define unless(c) if(!(c))
#define until(c) while(!(c))
#define loop while(true)

int main(){
    int L, N;
    scanf("%d %d", &L, &N);
    vector<int> s0, s1, b0, b1; // /:s \:b
    times(N, i){
        int X, Y;
        scanf("%d %d", &X, &Y);
        if(X % 2 == Y % 2){
            s0.push_back(X - Y);
            b0.push_back(X + Y - (L - 1));
        }else{
            s1.push_back(X - Y);
            b1.push_back(X + Y - (L - 1));
        }
    }
#define unique_sort(v) sort(v.begin(), v.end()); v.erase(unique(v.begin(), v.end()), v.end())
    unique_sort(s0);
    unique_sort(s1);
    unique_sort(b0);
    unique_sort(b1);
    long long ans = 0;
    times(s0.size(), i){
        ans += L - abs(s0[i]);
    }
    times(b0.size(), i){
        ans += L - abs(b0[i]) - distance(upper_bound(s0.begin(), s0.end(), -L + abs(b0[i])),
                                         lower_bound(s0.begin(), s0.end(),  L - abs(b0[i])));
    }
    times(s1.size(), i){
        ans += L - abs(s1[i]);
    }
    times(b1.size(), i){
        ans += L - abs(b1[i]) - distance(upper_bound(s1.begin(), s1.end(), -L + abs(b1[i])),
                                         lower_bound(s1.begin(), s1.end(),  L - abs(b1[i])));
    }
    printf("%lld\n", ans);
    return 0;
}