Which U.S. president died in 1841 of pneumonia after only being in office for about a month?

Explanation

The 9th president of the USA, William Harrison, insisted that he did not need to wear an overcoat, even though it was a wet, cold and windy day the day he swore the presidential oath in 1841. He held a more than two-hour long speech, after which he drove in procession through the city. It is therefore no wonder that he suffered severe pneumonia. He died only a month later and was unconscious for most of the disease. With his 68 years, he was at the time the oldest president elected and also the president with the shortest term in office.