Math.Floor Method (Decimal)
Note 

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Returns the largest integer less than or equal to the specified decimal number.
Assembly: mscorlib (in mscorlib.dll)
Parameters
 d

Type:
System.Decimal
A decimal number.
Return Value
Type: System.DecimalThe largest integer less than or equal to d. Note that the method returns an integral value of type Math.
The behavior of this method follows IEEE Standard 754, section 4. This kind of rounding is sometimes called rounding toward negative infinity. In other words, if d is positive, any fractional component is truncated. If d is negative, the presence of any fractional component causes it to be rounded to the smaller integer. The operation of this method differs from the Ceiling method, which supports rounding toward positive infinity.
The following example illustrates the Math.Floor(Decimal) method and contrasts it with the Ceiling(Decimal) method.
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1