#include<fstream.h>
#include<iostream.h>
#include<math.h>
int main(void)
{
fstream f("stergeri.in", ios::in);
fstream g("stergeri.out", ios::out);
long n,m,k,v[2000],a,b,x,y,l;
f>>n>>m>>k;
a=b=x=y=0;
while (m)
      { f>>a>>b;
	if (a<=k)
	   l=k+labs(a-(b+labs(x-y)+1))+1;
	   else
	   l=k;
	x=a;
	y=b;
        m--;
      }
f.close();
g<<l<<"\n";
g.close();
return 0;
}