import std.stdio, std.string, std.conv;
import std.typecons;
import std.algorithm, std.array, std.range, std.container;
import std.math;

void main() {
    auto ABN = readln.split.to!(long[]);
    auto A = ABN[0], B = ABN[1], N = ABN[2];
    auto x = min(B-1, N);
    writeln(cast(long) (floor(cast(double) A * cast(double) x / cast(double) B) - A * cast(double) floor(cast(double) x / cast(double) B)));
}

