# calculating beta for elgamal elliptic curves [duplicate]

Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime $p$, an elliptic curve $E$, a point $\alpha$ on $E \pmod p$, and a secret integer $f$. Suppose that Bob has selected $p =8115633240307$; $E: y^2 = x^3 + 45x + 1$; $\alpha = (1728910711, 274151521448)$, $f=7$; How would we calculate $\beta = [f]\alpha = [7](1728910711, 274151521448)$?.