import std;

long calc(long a, long b, long n) {
    long x = min(b-1, n);
    return a * x / b;
}

void main() {
    long a, b, n; scan(a, b, n);
    writeln(calc(a, b, n));
}

void scan(T...)(ref T a) {
    string[] ss = readln.split;
    foreach (i, t; T) a[i] = ss[i].to!t;
}
T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;
