Let\(\overrightarrow{a},\overrightarrow{b},\overrightarrow{c}\)be three vectors such that | \(\overrightarrow{a}\) |= 3, | \(\overrightarrow{b}\) |= 4, | \(\overrightarrow{c}\) |= 5 and each one of them being perpendicular to the sum of the other two, find | \(\overrightarrow{a}+\overrightarrow{b}+\overrightarrow{c}\) |.