When a specimen of $M25$ concrete is loaded to a stress level of $12.5 \: MPa$, a strain of $500 \times 10^{-6}$ is recorded. If this load is allowed to stand for a long time, the strain increases to $1000 \times 10^{-6}$. In accordance with the provisions of $IS:456-2000$, considering the long-term effects, the effective modulus of elasticity of the concrete (in $MPa$) is _________