Database: world_development_indicators
Question: In 1960, what is largest population for country with upper middle income?
SQL: SELECT MAX(T2.Value) FROM Country AS T1 INNER JOIN Indicators AS T2 ON T1.CountryCode = T2.CountryCode WHERE T1.IncomeGroup = 'Upper middle income' AND T2.Year = 1960 AND T2.IndicatorName = 'Population, total'