51Nod-1499-图

#include <cstdio>
#include <algorithm>
#include <cmath>

using namespace std;

int n, m, ans = 0;

template <class T>
inline void scan_d(T &ret)
{
    char c;
    ret = 0;
    while ((c = getchar()) < '0' || c > '9');
    while (c >= '0' && c <= '9')
    {
        ret = ret * 10 + (c - '0'), c = getchar();
    }
}

int main()
{
    scanf("%d%d", &n, &m);

    //  全放 A 集合
    int x, y;
    for (int i = 1; i <= m; i++)
    {
        scan_d(x);
        scan_d(y);
        ans += abs(x - y);
    }

    //  全放 B 集合
    int sum = 0;
    for (int i = 1; i <= n; i++)
    {
        for (int j = i + 1; j <= n; j++)
        {
            sum += j - i;
        }
    }
    ans = max(ans, sum - ans);

    printf("%d\n", ans);

    return 0;
}