In the circuit shown in figure $C_1=1\mu F$  and ${\mathrm{C}}_2=2\mu \mathrm{F}$ . Capacitor ${\mathrm{C}}_1$  is charged to $100V$ and $C_2$ is charged to $20V$  . After charging they are connected as shown. When the switches $S_1,S_2$  and $S_3$ all are closed, the charge flowing through $S_1$ is