static void Main()
{
var n = long.Parse(Console.ReadLine());
var x = (FloorSqrtDec()(9 + 8 * n) - 1) / 2;
Console.WriteLine(n + 1 - x);
}
public static bool IsSquareNumberDec(decimal x)
{
decimal r = FloorSqrtDec()(x);
return(r * r == x);
}
