var d1,n,m,k,i,i1,i2,x,y,x1,y1,d:longint;
    f,g:text;
begin
assign(f,'stergeri.in');reset(f);
assign(g,'stergeri.out');rewrite(g);
read(f,n,m,k);
read(f,x,y);
x1:=x;
y1:=y;
d:=y-x+1;
for i:=2 to m do begin
    read(f,x,y);
    i1:=x;
    i2:=y;
    if x1<=i1+d then i1:=i1+d;
    if y1<=i2+d then i2:=i2+d;
    x1:=i1;
    y1:=i2;
    d1:=d;
    d:=i2-i1+1+d;
    end;
writeln(g,d+k);
close(f);
close(g);
end.