Complete rational arithmetic sums

Let {itq} > 1 be an integer number, \(f\left( x \right) = {a_n}{x^n} + \ldots + {a_1}x + {a_0}\) be a polynomial with integer coefficients, and ({ita}{in{itn}}, . . . ,{ita}{in1},{itq}) = 1. The following estimate is valid: \(\left| {S\left( {\frac{{f\left( x \right)}}{q}} \right)} \right| = \left| {\sum\limits_{x = 1}^q \rho \left( {\frac{{f\left( x \right)}}{q}} \right)} \right| \ll {q^{1 - 1/n}}\), where \(\rho \left( t \right) = 0,5 - \left\{ t \right\}\).