Well... If this has to be the case, I fear I may not be able to help precisely. Still, as per http://cararac.com/engine_oil/suzuki/alto.html , the recommended oil grades for F8B engine are 10w40 and 15w40, with 2.7L quantity.
I would suggest to go for 10w40 from any reputed brand, but ensure that oil is
% genuine and original. You may check Caltex, ZIC, Shell and Total, but ensure compatible API rating and Semi Synthetic, Fully Synthetic, Mineral, etc. Thing.