At Eurocrypt 1993, Brands and Chaum introduced distance bounding protocols to defend against mafia fraud attack and distance fraud attack. A distance bounding protocol usually consists of n rounds of a single-bit challenge and a single-bit response, which determines the distance between communicating entities by measuring the round-trip time of signals. Let FARM and FARD be the false acceptance rate against the mafia fraud attack and the distance fraud attack, respectively. The state-of-the-art distance bounding protocols in terms of the false acceptance rate have either (FARM,FARD) = ((1/2)n, (1/2)n) or (FARM,FARD) = (4(3/8)n, (7/8)n). We introduce a flexible distance bounding protocol whose false acceptance rate (FARM,FARD) can be chosen from ((1/2)n, (1/2)n) to ((1/4)n, (3/4)n).