int main()
{
    int a,b;
    scanf("%d %d",&a,&b);
    int tree[10009];
    int sum=0;
    for(int i=0;i<b;i++){
        int n,m;
        scanf("%d %d",&n,&m);
        for(int j=n;j<=m;j++)
        {
            tree[j]=1;
        }
    }
    for (int i=0;i<=a;i++){
        sum+=tree[i];
    }

    printf("%d",a+1-sum);
}