$20 \mathrm{~mL}$ of calcium hydroxide was consumed when it was reacted with $10 \mathrm{~mL}$ of unknown solution of $\mathrm{H}_{2} \mathrm{SO}_{4}$. Also $20 \mathrm{~mL}$ standard solution of $0.5 ~\mathrm{M} ~\mathrm{HCl}$ containing 2 drops of phenolphthalein was titrated with calcium hydroxide, the mixture showed pink colour when burette displayed the value of $35.5 \mathrm{~mL}$ whereas the burette showed $25.5 \mathrm{~mL}$ initially. The concentration of $\mathrm{H}_{2} \mathrm{SO}_{4}$ is _____________ M. (Nearest integer)