#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
using namespace std;
typedef long long LL;
int n,f[1010],s,r;
LL p,minn;
struct na
{
	int m,n;
} e[10010];
int main()
{
	minn=10000;
	cin>>n>>p;
	for(int i=1;i<=p;i++)
	{
		
		scanf("%d%d",&e[i].m,&e[i].n);
		if(e[i].m==e[i].n)
		{
			i--;
			p--;
		}
		if(e[i].m>e[i].n)
		swap(e[i].m,e[i].n);
	}
	for(int k=1;k<=n;k++) // 断开[k,k+1];
	{
		int ans=0;
		int pan=0;
		r=0;
		memset(f,0,sizeof(f));
		for(int i=1;i<=p;i++)
		{
			if(e[i].m<=k&&e[i].n>=k+1)
			{
				f[1]=max(f[1],e[i].m);
				f[e[i].n]=max(f[e[i].n],n+1);
			}
			else
			f[e[i].m]=max(f[e[i].m],e[i].n);
		}
		for(int i=1;i<=n;i++)
		{
			if(f[i]==0) continue;
			if(i>r){
			ans+=f[i]-i;
			r=f[i];
		    }
		    else if(f[i]>r)
		    {
		    	ans+=f[i]-r;  
                r=f[i];
            }
            if(ans>minn)
            break;
	    }
	    if(ans<minn)
	    minn=ans;
	}
	cout<<minn;
	return 0;
}

/*
5 3
4 2
1 3
5 4
*/