//live_100.cpp
#include<stdio.h>
#include<algorithm>
using namespace std;
typedef long long ll;

int main()
{
	ll n;
	int s;
	ll ans = 0;
	static ll t[100005] = {0};
	
	scanf("%lld%d", &n, &s);
	
	for(int i = 0; i < s; ++i)
	{
		int x, y;
		scanf("%d%d", &x, &y);
		++t[x];
		--t[y + 1];
	}
	for(int i = 1; i <= 100000; ++i)
	{
		t[i] += t[i - 1];
		ans += min(t[i], n);
	}
	printf("%lld\n", ans);
	return 0;
}