#include <stdio.h>

int main(void) {
  double a,b,n;
  scanf("%lf %lf %lf",&a,&b,&n);
  unsigned long int max,f1,f2;
  max=0;
  for(double x=0;x<=n;x++){
    if(x/b-(int)(x/b)<0.7) continue;
    f1=(int)(a*x/b);
    f2=(int)(x/b);
    if(max<(f1-a*f2)) max=f1-a*f2;
  }
  printf("%ld",max);
  return 0;
}
