const lines = require('fs').readFileSync('/dev/stdin', 'utf8')
const line = lines.split(' ')
const A = +line[0]
const B = +line[1]
const N = +line[2]

let max = 0;
for (let x = 0; x <= N; x++) {
    const v = Math.floor((A * x) / B) - (A * Math.floor(x / B))
    max = max < v ? v : max;
}

console.log(max)