#include <stdio.h>
#include <math.h>

int main(int argc, const char **argv)
{
    double a = 0, b = 0, n = 0, loop = 1, max = 0, calc = 0;

    fscanf(stdin, "%lf %lf %lf", &a, &b, &n);

    for ( loop = 1; loop <= n; loop++ )
    {
        calc = floor( a * loop / b ) - a * floor( loop / b );
        if ( calc > max ) max = calc;
    }

    fprintf(stdout, "%ld\n", (long)max);
    return 0;
}