Some Basic Concepts of Chemistry Part 2

20‌mL of calcium hydroxide was consumed when it was reacted with 10‌mL of unknown solution of H2SO4. Also 20‌mL standard solution of 0.5‌MHCl containing 2 drops of phenolphthalein was titrated with calcium hydroxide, the mixture showed pink colour when burette displayed the value of 35.5‌mL whereas the burette showed 25.5‌mL initially. The concentration of H2SO4 is _______ M.(Nearest integer)