Question: How many number 1 hits did the performer of Monsters of Rock Tour 1988 have?

full_context: Document 1: Hard rock: In the new commercial climate glam metal bands like Europe, Ratt, White Lion and Cinderella broke up, Whitesnake went on hiatus in 1991, and while many of these bands would re-unite again in the late 1990s or early 2000s, they never reached the commercial success they saw in the 1980s or early 1990s. Other bands such as Mötley Crüe and Poison saw personnel changes which impacted those bands' commercial viability during the decade. In 1995 Van Halen released Balance, a multi-platinum seller that would be the band's last with Sammy Hagar on vocals. In 1996 David Lee Roth returned briefly and his replacement, former Extreme singer Gary Cherone, was fired soon after the release of the commercially unsuccessful 1998 album Van Halen III and Van Halen would not tour or record again until 2004. Guns N' Roses' original lineup was whittled away throughout the decade. Drummer Steven Adler was fired in 1990, guitarist Izzy Stradlin left in late 1991 after recording Use Your Illusion I and II with the band. Tensions between the other band members and lead singer Axl Rose continued after the release of the 1993 covers album The Spaghetti Incident? Guitarist Slash left in 1996, followed by bassist Duff McKagan in 1997. Axl Rose, the only original member, worked with a constantly changing lineup in recording an album that would take over fifteen years to complete.
Document 2: Queen (band): The band have released a total of eighteen number one albums, eighteen number one singles, and ten number one DVDs worldwide, making them one of the world's best-selling music artists. Queen have sold over 150 million records, with some estimates in excess of 300 million records worldwide, including 34.5 million albums in the US as of 2004. Inducted into the Rock and Roll Hall of Fame in 2001, the band is the only group in which every member has composed more than one chart-topping single, and all four members were inducted into the Songwriters Hall of Fame in 2003. In 2009, "We Will Rock You" and "We Are the Champions" were inducted into the Grammy Hall of Fame, and the latter was voted the world's favourite song in a global music poll.
Document 3: Damaged Justice: Damaged Justice was the fourth concert tour by the American thrash metal band Metallica. It began on September 11, 1988 and ended on October 8, 1989. The name is believed to be inspired either by the cover of its fourth studio album "...And Justice for All", or by the song "Damage, Inc." from the group's previous album, "Master of Puppets".
Document 4: Hard rock: From outside the United Kingdom and the United States, the Canadian trio Rush released three distinctively hard rock albums in 1974–75 (Rush, Fly by Night and Caress of Steel) before moving toward a more progressive sound with the 1976 album 2112. The Irish band Thin Lizzy, which had formed in the late 1960s, made their most substantial commercial breakthrough in 1976 with the hard rock album Jailbreak and their worldwide hit "The Boys Are Back in Town", which reached number 8 in the UK and number 12 in the US. Their style, consisting of two duelling guitarists often playing leads in harmony, proved itself to be a large influence on later bands. They reached their commercial, and arguably their artistic peak with Black Rose: A Rock Legend (1979). The arrival of Scorpions from Germany marked the geographical expansion of the subgenre. Australian-formed AC/DC, with a stripped back, riff heavy and abrasive style that also appealed to the punk generation, began to gain international attention from 1976, culminating in the release of their multi-platinum albums Let There Be Rock (1977) and Highway to Hell (1979). Also influenced by a punk ethos were heavy metal bands like Motörhead, while Judas Priest abandoned the remaining elements of the blues in their music, further differentiating the hard rock and heavy metal styles and helping to create the New Wave of British Heavy Metal which was pursued by bands like Iron Maiden, Saxon and Venom.
Document 5: Monsters of Rock Tour 1988: The Monsters of Rock Tour 1988 was a festival tour headlined by hard rock band Van Halen as part of their promotion for their "OU812" album. The Scorpions were a co-headliner. Opening bands included Metallica, Dokken, and Kingdom Come. It formed the first section of the OU812 Tour, the main part of which followed immediately after Monsters of Rock 1988. As one of the many well-known Monsters of Rock tours, the tour featured an impressive line-up, especially for a single-day event, and proved very popular.
Document 6: Hard rock: Established bands made something of a comeback in the mid-1980s. After an 8-year separation, Deep Purple returned with the classic Machine Head line-up to produce Perfect Strangers (1984), which reached number five in the UK, hit the top five in five other countries, and was a platinum-seller in the US. After somewhat slower sales of its fourth album, Fair Warning, Van Halen rebounded with the Top 3 album Diver Down in 1982, then reached their commercial pinnacle with 1984. It reached number two on the Billboard album chart and provided the track "Jump", which reached number one on the singles chart and remained there for several weeks. Heart, after floundering during the first half of the decade, made a comeback with their eponymous ninth studio album which hit number one and contained four Top 10 singles including their first number one hit. The new medium of video channels was used with considerable success by bands formed in previous decades. Among the first were ZZ Top, who mixed hard blues rock with new wave music to produce a series of highly successful singles, beginning with "Gimme All Your Lovin'" (1983), which helped their albums Eliminator (1983) and Afterburner (1985) achieve diamond and multi-platinum status respectively. Others found renewed success in the singles charts with power ballads, including REO Speedwagon with "Keep on Loving You" (1980) and "Can't Fight This Feeling" (1984), Journey with "Don't Stop Believin'" (1981) and "Open Arms" (1982), Foreigner's "I Want to Know What Love Is", Scorpions' "Still Loving You" (both from 1984), Heart’s "What About Love" (1985) and "These Dreams" (1986), and Boston's "Amanda" (1986).
Document 7: Scorpions (band): On the Savage Amusement tour in 1988, the Scorpions became only the second Western group (not American) to play in the Soviet Union. Uriah Heep had performed in December 1987 in Leningrad. The following year the band returned to perform at the Moscow Music Peace Festival. As a result, the Scorpions developed an extended Russian fan base and still return to perform. Also in 1989, Scorpions released the compilation album Best of Rockers 'n' Ballads, which, in addition to the band's hits from 1979 to 1988, included several rare or previously unreleased tracks: "Hey You", from the Animal Magnetism sessions; the re-recorded "long version" of "Is There Anybody There?"; and a cover of The Who's "I Can't Explain", which was also included on that same year's Stairway to Heaven/Highway to Hell charity compilation album. This is the Scorpions' only compilation album to be certified platinum in the United States.Wishing to distance themselves from the Savage Amusement style, the band separated from their long-time producer and "Sixth Scorpion", Dieter Dierks, replacing him with Keith Olsen when they returned to the studio in 1990. Crazy World was released that year and displayed a less polished sound. The album was propelled in large part by the massive success of the ballad "Wind of Change". The song muses on the socio-political changes that were occurring in Eastern Europe and other parts of the world at the end of the Cold War. Crazy World is the band's last album to receive gold or platinum certification in the United States. On 21 July 1990 they joined many other guests for Roger Waters' massive performance of The Wall in Berlin. Scorpions performed both versions of "In the Flesh" from The Wall.
Document 8: The Best of Both Worlds (Van Halen album): The Best of Both Worlds is the second greatest hits album by American hard rock band Van Halen, released on July 20, 2004 on Warner Bros. The compilation features material recorded with lead vocalists David Lee Roth and Sammy Hagar, but omitting Gary Cherone's three-year tenure with the band. Prior to "The Best of Both Worlds"' release, Hagar reunited with Van Halen, and the band subsequently recorded three new tracks to include on the release.
Document 9: Van Halen discography: As of 2007, Van Halen has sold 75 million albums worldwide and have had thirteen No. 1 hits on the Billboard Mainstream Rock chart. During the 1980s they also had more Billboard Hot 100 hits than any other hard rock or heavy metal band. According to the RIAA, Van Halen is the nineteenth best - selling band / artist of all time with sales of over 56 million albums in the US, and is one of five rock bands that have had two albums (Van Halen and 1984) sell more than ten million copies in the US.
Document 10: Hard rock: With the rise of disco in the US and punk rock in the UK, hard rock's mainstream dominance was rivalled toward the later part of the decade. Disco appealed to a more diverse group of people and punk seemed to take over the rebellious role that hard rock once held. Early punk bands like The Ramones explicitly rebelled against the drum solos and extended guitar solos that characterised stadium rock, with almost all of their songs clocking in around two minutes with no guitar solos. However, new rock acts continued to emerge and record sales remained high into the 1980s. 1977 saw the début and rise to stardom of Foreigner, who went on to release several platinum albums through to the mid-1980s. Midwestern groups like Kansas, REO Speedwagon and Styx helped further cement heavy rock in the Midwest as a form of stadium rock. In 1978, Van Halen emerged from the Los Angeles music scene with a sound based around the skills of lead guitarist Eddie Van Halen. He popularised a guitar-playing technique of two-handed hammer-ons and pull-offs called tapping, showcased on the song "Eruption" from the album Van Halen, which was highly influential in re-establishing hard rock as a popular genre after the punk and disco explosion, while also redefining and elevating the role of electric guitar.
Document 11: List of best-selling albums: Michael Jackson's Thriller, estimated to have sold 65 million copies worldwide, is the best - selling album. Although sales estimates for Thriller have been as high as 120 million copies, these sales figures are unreliable. Jackson also currently has the highest number of albums on the list with five, while The Beatles and Madonna each have three.
Document 12: Hard rock: Bon Jovi's third album, Slippery When Wet (1986), mixed hard rock with a pop sensitivity and spent a total of 8 weeks at the top of the Billboard 200 album chart, selling 12 million copies in the US while becoming the first hard rock album to spawn three top 10 singles — two of which reached number one. The album has been credited with widening the audiences for the genre, particularly by appealing to women as well as the traditional male dominated audience, and opening the door to MTV and commercial success for other bands at the end of the decade. The anthemic The Final Countdown (1986) by Swedish group Europe was an international hit, reaching number eight on the US charts while hitting the top 10 in nine other countries. This era also saw more glam-infused American hard rock bands come to the forefront, with both Poison and Cinderella releasing their multi-platinum début albums in 1986. Van Halen released 5150 (1986), their first album with Sammy Hagar on lead vocals, which was number one in the US for three weeks and sold over 6 million copies. By the second half of the decade, hard rock had become the most reliable form of commercial popular music in the United States.
Document 13: Metallica: This Monster Lives: The book follows the emotional roller-coaster both he and his film partner Bruce Sinofsky and the band Metallica went through during the creation film. The book takes in the time from Berlinger and Sinofsky's first meeting with Metallica in 1999 to the 2003 Summer Sanitarium Tour. Berlinger and Sinofsky's relationship was at an all time low, exacerbated by Berlinger's decision to direct the disastrous sequel to the Blair Witch. At the start of filming the relationship between the band members, especially between vocalist James Hetfield and drummer Lars Ulrich, is in a similarly perilous position after bassist Jason Newsted quit the band and long standing grudges between the remaining members threaten to escalate past the point of no return.
Document 14: Van Halen (album): Van Halen is the debut studio album by American hard rock band Van Halen. Released on February 10, 1978, the album peaked at # 19 on the Billboard 200. The album became widely recognized as the band's popularity grew, selling more than 10 million copies in the United States by August 7, 1996 and being certified Diamond.
Document 15: Guns N' Roses/Metallica Stadium Tour: The Guns N' Roses/Metallica Stadium Tour was a co-headlining concert tour by American rock bands Guns N' Roses and Metallica during 1992. It took place in the middle of Guns N' Roses' "Use Your Illusion Tour," promoting their "Use Your Illusion I" & "II" albums, and between Metallica's "Wherever We May Roam Tour" and "Nowhere Else to Roam," promoting their eponymous fifth album "Metallica". The tour's opening act was Faith No More. Axl Rose had wanted Seattle rock band Nirvana to be the opening act, but frontman Kurt Cobain refused.
ground_truth: thirteen
sub_queries: Monsters of Rock Tour 1988 >> performer Answer: Van Halen
how many number 1 hits did Van Halen have Answer: thirteen