“I’m not a magician, or a saviour,” Sergio Massa, the third person to take charge of Argentina’s economy in barely a month, said on Wednesday. “The challenge is enormous.” In his first speech since being appointed last week, Massa, 50, announced a slate of measures including a vow to end money printing to fund the budget — financing it instead through deficit reduction or private-sector borrowing — along with building dollar reserves and “reworking” state subsidies in order to narrow the country’s large deficit and meet budget targets.