Combine multiple dictionaries into a single dictionary [duplicate]

var d1 = new Dictionary<string, int>();
var d2 = new Dictionary<string, int>();
var d3 = new Dictionary<string, int>();

var result = d1.Union(d2).Union(d3).ToDictionary (k => k.Key, v => v.Value);

EDIT
To ensure no duplicate keys use:

var result = d1.Concat(d2).Concat(d3).GroupBy(d => d.Key)
             .ToDictionary (d => d.Key, d => d.First().Value);