How to add new row in dataframe : I have two dataframe that look like 

df1

          V1      V2     V3     V4
    rs200140498	chr1	861315	GG
    rs371217242	chr1	861329	AA
    rs200686669	chr1	861349	CC
    rs370046315	chr1	861357	CC
    rs374110379	chr1	861521	GG
    rs74045401	chr1	861530	GG
    rs377418023	chr1	865394	CC
    rs79027658	chr1	865438	CC
    rs202189913	chr1	865488	AA
    rs370992396	chr1	865543	GG
and df2

          V1      V2     V3     V4
    rs200140498	chr1	861315	GG
    rs200686669	chr1	861349	CC
    rs370046315	chr1	861357	CC
    rs74045401	chr1	861530	GG
    rs377418023	chr1	865394	CC
    rs202189913	chr1	865488	AA
    rs370992396	chr1	865543	GG
And i want to compare its and get new data frame 

              V1      V2     V3     V4
     rs200140498	chr1	861315	GG
     rs371217242	chr1	861329	--
     rs200686669	chr1	861349	CC
     rs370046315	chr1	861357	CC
     rs374110379	chr1	861521	--
     rs74045401	    chr1	861530	GG
     rs377418023	chr1	865394	CC
     rs79027658	    chr1	865438	--
     rs202189913	chr1	865488	AA
     rs370992396	chr1	865543	GG
Can anyone help me with this?

Thanks in advance.