let i = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n').slice(1, -1)
let r = 0
i.forEach((e) => {
  let x = []
  e.split(' ').forEach((n) => x.push(n.split(':').map((m) => parseInt(m))))
  let a = [x[1][0] - x[0][0], x[1][1] - x[0][1]]
  if (a[0] < 0 || (a[0] == 0 && a[1] < 0)) a[0] += 24
  r += a[0] * 60 + a[1]
})
console.log(r)