How to define Int64 field type ? Undefined type Int64

[khanakia]

I can see gqlgen.yml has these model assigned

 Int:
    model:
      - github.com/99designs/gqlgen/graphql.Int
      - github.com/99designs/gqlgen/graphql.Int64
      - github.com/99designs/gqlgen/graphql.Int32

input Student {
  Id: Int64
  name: String
}

But when I define the Int64 above I get the following error

failed to load schema: graph/schema.graphqls:30: Undefined type Int64.
exit status 1