#include <bits/stdc++.h>

#include <cstdio>

#include <cmath>

#define rep(i, a, b) for(int i = a; i <= b; i++)

#define min(a, b) ((a) < (b) ? (a) : (b))

#define max(a, b) ((a) > (b) ? (a) : (b))

int gcd(int a, int b){return b == 0 ? a : gcd(a%b, a);}

const int N = 10011;

int main()

{

    int L, M, a, b, c[N];

    scanf("%d %d", &L, &M);

    rep(i, 0, L) c[i] = 1;

    while(M--)

    {

        scanf("%d %d", &a, &b);

        rep(i, a, b) c[i] = 0;

    }

    c[10010] = 0;

    rep(i, 0, L) c[10010] += c[i];

    printf("%d\n", c[10010]);

    return 0;

}