Assign different name for property during serialization in JSON

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C#

C#4.0

JSON.NET

How we can assign different name for property during serialization in JSON.
Eg. My class have following structure

public class std
{
public int no {get;set;}
public string name {get;set;}
public string add {get;set;}
}

During json serialization (at run time) i wants name s1 for first property(no),s2 for second property (name) and s3 for third property (add).

i found mechanism that i can use attribute [JsonProperty(PropertyName = "S1")]
at time of declaration.

but my requirement assign different name during serialization(At run time).
i am using JSON with C#.

Thanks in advance.