Can somebody tell me how much you would need to be near smokers to get killed or get cancer from secondhand smoking?

No simple answer: But cases where people have gotten cancers related to smoking from second hand smoke involved very high level exposure over long periods of time - people working in bars/restaurants where there was lots of smoke, people living with smokers in the household who smoked indoors etc. Casual exposures from time to time are unlikely to cause any major or permanent harm, and certainly not getting killed.