#include <stdio.h>
#define M 200
int main()
{
int i,m,l,n=0,a[M],h,end;
scanf("%d%d",&l,&m);
for(i=0;i<2*m;i++)
scanf("%d",&a[i]);
n=1+a[1]-a[0];
for(i=2;i<2*m;i+=2)
{
h=a[i-2];
end=a[i-1];
if(a[i]>end)
{
n+=1+a[i+1]-a[i];

continue;
}
if(a[i]<h&&a[i+1]<end)
{
n+=h-a[i];
continue;
}
if(a[i+1]>end&&a[i]>h)
{
n+=a[i+1]-end;
continue;

}
if(a[i]<h&&a[i+1]>end)
{
n+=(h-a[i])+(a[i+1]-end);

continue;
}

}
printf("%d",l+1-n);

return 0;
}