const input = require("fs").readFileSync("/dev/stdin", "utf8")

;(input => {
    const [A, B, N] = input.split(' ').map(n => n - 0)
    console.log(A, B, N)
    let x = 0
    if (N >= B) {
        x = B - 1
    } else {
        x = N
    }
    const res = Math.floor(A * x / B)
    console.log(res)
})(input)
