import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.bigint, std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
static string[] s_rd;
T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); }
double euDist(T)(T[] a, T[] b) { auto c = a.dup; c[] -= b[]; c[] *= c[]; return sqrt(cast(double)c.sum); }
double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; }
double norm(double[] vec) { return sqrt(reduce!((a,b)=>a+b*b)(0.0, vec)); }
double dotProd(double[] a, double[] b) { auto r = a.dup; r[] *= b[]; return r.sum; }

long mod = 10^^9 + 7;
//long mod = 998_244_353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }
void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }
void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); }

long compress(in long[] arr, out long[long] zip, out long[] unzip)
{
	auto index = MAKE_IDX(arr);
	long last = arr[index[0]], x;
	zip[last] = x;
	unzip ~= last;
	foreach (i; index[1..$])
	{
		if (arr[i] == last) continue;
		last = arr[i];
		++x;
		zip[last] = x;
		unzip ~= last;
	}
	return x+1;
}

void main()
{
	auto N = RD;
	auto M = RD;
	auto A = new long[](M);
	auto B = new long[](M);
	bool[long] set;
	foreach (i; 0..M)
	{
		A[i] = RD-1;
		B[i] = RD-1;
		set[A[i]] = true;
		set[B[i]] = true;
	}
	
	long[long] zip;
	long[] unzip;
	auto len = compress(set.keys, zip, unzip);
	auto dp = new long[](len);
	foreach (i; 0..len)
		dp[i] = unzip[i] * 2;

	long ans = long.max;
	long[][] arr;
	foreach (i; 0..M)
	{
		arr ~= [A[i], i, 0];
		arr ~= [B[i], i, 1];
	}
	arr.sort!"a[0] < b[0]";
	long lastP, lastC;
	foreach (e; arr)
	{
		auto i = e[1];
		auto num = e[2];
		auto u = zip[A[i]];
		auto v = zip[B[i]];
		if (num == 0)
		{
			dp[u].chmin(lastC + (A[i] - lastP)*2);
			lastP = A[i];
			lastC = dp[u];
			auto c = (B[i] - A[i]) * 2 - 1;
			dp[v].chmin(dp[u]+c);
			ans.chmin((N-1 - A[i]) * 2 + dp[u]);
		}
		else
		{
			dp[v].chmin(lastC + (B[i] - lastP)*2);
			lastP = B[i];
			lastC = dp[v];
			ans.chmin((N-1 - B[i]) * 2 + dp[v]);
		}
	}

	writeln(ans);
	stdout.flush;
	debug readln;
}