All elections in the Czech Republic are based on the principle of universal suffrage. Any adult citizen who is at least 18 years old can vote, except those who have been stripped of their legal capacities by a court, usually on the basis of mental illness. Elected representatives are elected directly by the citizens without any intermediaries. Election laws are not part of the constitution, but – unlike regular laws – they cannot be changed without the consensus of both houses of the Parliament. The Czech Republic uses a two-round plurality voting system for the presidential and Senate elections and an open party-list proportional representation system for all other elections. The proportional representation system uses the D'Hondt method for allocating seats. Elections are usually held over two days, from 14:00 to 22:00 on Friday and then from 8:00 to 14:00 on Saturday. System of elections Presidential elections Any citizen aged 40 or over can stand for president, unless they have already served two terms in the office or have been found guilty of treason by the Constitutional Court. From 1993 to 2008, presidents were elected by both houses of the Parliament in three rounds of voting. Since the 2013 election the president is elected directly by the people in two rounds, where the top two candidates from the first round face each other again in the second round. Presidents are elected for five-year terms. Chamber of Deputies elections Any citizen aged 21 or over can stand as a candidate for the Chamber of Deputies, which consists of 200 members elected for four-year terms. The Chamber of Deputies elections do not necessarily take place at fixed intervals as the Chamber of Deputies can be prematurely dissolved by the president, under conditions set by the Constitution. The president also decides the date of the elections, thereby starting the official election campaign, during which political parties' spending is capped by the law. There are 14 voting districts for elections to the Chamber of Deputies, which correspond to the regions of the Czech Republic. Each of these voting districts has a different number of seats available, and parties submit ranked lists of candidates for each district. Candidates of a political party can only win a seat if their party received at least 5% of all valid votes nationally. Voters must choose only one political party to vote for, but they may use up to