Calculate NDVI from sentinel 2

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Copy the code below and fill out the ??

// import image
var img = ee.Image("COPERNICUS/S2/20170410T022321_20170410T022324_T51PWP");
// calculate ndvi
var ndvi = img.normalizedDifference(["??","??"]);

// add image
Map.addLayer(img,{bands:"??,??,??",min:0,max:3000},"true color image");
// add NDVI
Map.addLayer(ndvi,{palette:"blue,red,yellow,green,darkgreen",min:??,max:??},"ndvi");

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