using namespace std;
#define Maxn 10000
struct Node
{
int a,b,left,right,cover;
};
Node Tree[Maxn];
int Number,Tot,c,d;
void build(int a,int b)
{
int Now;
Tot++;
Now=Tot;
Tree[Now].a=a;
Tree[Now].b=b;
Tree[Now].cover=0;
if(b-a>1)
{
int mid=(a+b)>>1;
Tree[Now].left=Tot+1;
build(a,mid);
Tree[Now].right=Tot+1;
build(mid,b);
}
}
void insert(int Num)
{
if(c<=Tree[Num].a&&Tree[Num].b<=d)
Tree[Num].cover++;
else
{
int mid=(Tree[Num].a+Tree[Num].b)>>1;
if(c<=mid)
insert(Tree[Num].left);
if(d>=mid)
insert(Tree[Num].right);
}
}
void del(int Num)
{
if(c<=Tree[Num].a&&Tree[Num].b<=d)
Tree[Num].cover--;
else
{
int mid=(Tree[Num].a+Tree[Num].b)>>1;
if(c<=mid)
insert(Tree[Num].left);
if(d>=mid)
insert(Tree[Num].right);
}
}
void Count(int Num)
{
if(Tree[Num].cover)
Number+=(Tree[Num].b-Tree[Num].a);
else
{
if(Tree[Num].left)
Count(Tree[Num].left);
if(Tree[Num].right)
Count(Tree[Num].left);
}
}
int main()
{
scanf("%d%d",&c,&d);
build(c,d);
while(scanf("%d%d",&c,&d)!=EOF)
insert(1);
Number=0;
Count(1);
printf("%d\n",Number);
return 0;
}