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

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

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

    if ( b > n ) fprintf( stdout, "%ld\n", (long)( a * n / b ) );
    else fprintf( stdout, "%ld\n", (long)( a * (b - 1) / b ) );

    return 0;
}