import std;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] lreads(T = long)(long n){return generate(()=>readln.chomp.to!T()).take(n).array();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long A, B, N;
    scan(A, B, N);
    long ok = 1;
    long ng = N;
    while (1 < ng - ok)
    {
        long x = (ok + ng) / 2;
        long tmp1 = (A * x) / B - A * (x / B);
        long tmp2 = (A * (x + 1)) / B - A * ((x + 1) / B);
        if (tmp1 <= tmp2)
        {
            ok = x;
        }
        else
        {
            ng = x;
        }
    }
    long x = ng;
    writeln((A * x) / B - A * (x / B));
}
