It’s difficult to fathom how it is physically possible for any human to depart Hopkinton at 10:30 a.m. and eventually cross the finish line in Copley Square within the same week.The feeling of overwhelming satisfaction a runner receives upon completing the grueling, 26.22-mile Boston Marathon – a feeling so incomprehensible to so many – is one Salem’s Katie St. Pierre experienced last year.And she liked it so much she’s running again.”My boyfriend thinks I’m crazy,” she said. “It’s a mental thing. Being able to finish is such a rewarding experience. It’s awesome. That feeling of accomplishment is incredible.”St. Pierre, a 29-year-old financial analyst for Sylvania in Danvers, has trained year-round since 2003.Whether it’s in the company gym during her lunch break or outside when the conditions cooperate, St. Pierre runs six to seven miles a day, six days a week, or approximately 40 miles each week.She completed the marathon in five hours last year and is confident her time will drop significantly this trip through the course.”There was a nor’easter (last year). The weather was terrible,” she said. “My goal this year is four hours. It’s doable.”St. Pierre is not only running for her own sense of indescribable accomplishment, but also for the Boston-based charity Goodwill.In order to participate in the Boston Marathon, a female runner must qualify by completing the Chicago or New York Marathon in under 3:40.59 or compete in the name of a charity.Since St. Pierre has not had the opportunity to run in either of the aforementioned marathons (entrance into those are awarded through a lottery system), St. Pierre needed a charity she believed in.She found that in Goodwill.”I’ve always been interested in running a marathon, and I just needed to find a way in,” she said. “Goodwill provides programs for those with developmental disabilities and helps them find jobs.”Goodwill also operates a second-hand thrift store in order to provide job training, paid work opportunities, and low-cost quality goods to the community. St. Pierre, who also ran for Goodwill last year, donates her time to after-school program events in Roxbury and Dorchester and volunteers at the organization’s summer camp.With the help of family, friends and local businesses, St. Pierre had raised $1,700 as of this interview.”Every member of the Goodwill team is required to raise $3,000. If we don’t, the rest comes out of our pocket,” she said.Katie is not the only athlete in the St. Pierre clan. Her cousin, Brian, was a standout at St. John’s Prep and Boston College before being selected in the fifth round of the 2003 NFL draft by the Pittsburgh Steelers.He signed a one-year contract with the Arizona Cardinals on March 31.Those interested in aiding Katie St. Pierre’s quest for $3,000 may do so at www.firstgiving.com/ksaint9678 or can submit donations payable to Goodwill to Katie St. Pierre, 31 Symonds Street, No. 24, Salem, MA 01970.