#include <stdio.h>

int main(void) {
  double a,b,n;
  scanf("%lf %lf %lf",&a,&b,&n);
  unsigned long int max;
  max=0;
  for(double x=0;x<=n;x++){
    if(x/b-(int)(x/b)<0.5) continue;
    if(x/b-(int)(x/b)>0.9){
      max=(int)(a*x/b)-a*(int)(x/b);
      break;
    }
    if(max<((int)(a*x/b)-a*(int)(x/b))) max=(int)(a*x/b)-a*(int)(x/b);
  }
  printf("%ld",max);
  return 0;
}
