$50 \, cm^3$ of $0.2 \, N \, HCl$ is titrated against $0.1 \, N \, NaOH$ solution. The titration was discontinued after adding $50\, cm^3$ of $NaOH$. The remaining titration is completed by adding $0.5 \, N \, KOH$. The volume of $KOH$ required for completing the titration is