At \( 345 \,\mathrm{K} \), the half life for the decomposition of a sample of a gaseous compound initially at \( 55.5 \,\mathrm{kPa} \) was \( 340 \,\mathrm{s} \). When the pressure was \( 27.8 \,\mathrm{kPa} \), the half life was found to be \( 170 \,\mathrm{s} \). The order of the reaction is ____________. [integer answer]