Calculate the return of stocks.

Date 30/12/2020 04/01/2021 05/01/2021 06/01/2021 08/01/2021 11/01/2021 12/01/2021 13/01/2021 14/01/2021 15/01/2021 18/01/2021 19/01/2021 20/01/2021 RZD RU000A0JQ7Z2 97.79 97.89 97.92 97.92 97.87 97.88 97.57 97.45 97.68 97.65 97.54 97.5 97.46 QIWI RU000A1028C7 PRICE 97.13 96.89 96.2 96.31 96.02 95.8 95.81 95.59 95.35 95.19 95.04 95.33 95.39 PIK RU000A1026C1 97.39 97.34 97.32 97.1 97.09 96.9 96.8 96.61 96.46 96.39 96.36 96.2 96.23 Rusal RU000A101S81 96.41 96.01 95.94 95.76 95.5 94.79 94.96 94.44 93.97 93.82 93.56 94.17 94.46 MTS RU000A0ZYFC6 99.44 99.28 99.21 99.33 99.33 99.26 99.23 99.14 99.21 99.1 99.14 99.03 99.07