Program NoName;
var n,r,i:integer;
x: array [1..100] of real;
y: array [1..100] of real;
s,sg:real;
input,output:text;

begin
s:=0;
   assign(input, 'input.txt');
   reset(input);
   assign(output, 'output.txt');
   rewrite(output);


readln(n,r);
 if n=1 then writeln(1.00)else begin
   For i:=1 to n do
  readln(x[i],y[i]);
sg:=2*pi*r;
For i:=1 to n-1 do  s:=s+sqrt(sqr(x[i]-x[i+1])+sqr(y[i]-y[i+1]));
s:=s+sqrt(sqr(x[n]-x[1])+sqr(y[n]-y[1]));
s:=s+sg;
end;
writeln(s:1:2);
   close(input);
   close(output);
end.

First, remove the read and write in the txt files, you need to read/write from/to the console.
You'll get WA3 now.
Try to re-think the case when n=1; the answer is not always 1!