include[HTML_REMOVED]
define N 10000
int main()
{
int l,m,a[N],i,j,cnt=0;
scanf(“%d%d”,&l,&m);
for(i=0;i<=l;i)
a[i]=1;
for(i=0;i<m;i)
{
int b,c;
scanf(“%d%d”,&b,&c);
for(j=b;j<=c;j)
a[j]=0;
}
for(i=0;i<=l;i)
if(a[i])
cnt++;
printf(“%d”,cnt);
}