const input = require("fs").readFileSync("/dev/stdin", "utf8")
const lines = input.split('\n')
const [A, B, N] = lines[0].split(' ').map(Number)

let ans = 0
for (let x = 0; x <= N; x++) {
    const res = Math.floor(A * x / B) - A * Math.floor(x / B)
    ans = Math.max(ans, res)
}

console.log(ans)