var x, S: real;
n: integer;
begin
Read(x, n);
S := 0.0;
for var i := 1 to n do
S += i * Sin(x);
Write(S)
end.
var x, S: real;
n: integer;
begin
Read(x, n);
S := 0.0;
for var i := 1 to n do
S += i * Sin(x);
Write(S)
end.