{
TASK:stairs
LANG:PASCAL
}
var
n,k,i,l : integer;
a : array [1..100,1..2] of real;
min,otg : real;

procedure p(num:integer);
var
i : integer;
begin
a[num,1]:=a[num,1]+a[num+1,1];
a[num,2]:=a[num,2]+a[num+1,2];
for i:=num+1 to n-1 do begin a[i,1]:=a[i+1,1]; a[i,2]:=a[i+1,2]; end;
dec(n);
end;

procedure m;
var
i : integer;
r : real;
begin
l:=1;
min:=a[1,1]*a[2,2];
for i:=2 to n-1 do
begin
 r:=a[i,1]*a[i+1,2];
 if r<min then
 begin
  min:=r;
  l:=i;
 end;
end;
end;

begin
readln(n,k);
for i:=1 to n do readln(a[i,2],a[i,1]);
otg:=0;
repeat
m;
otg:=otg+min;
p(l);
until n<=k;
writeln(otg:0:3);
readln;
end.