#include<stdio.h>
int main(void){
  long long int a,b,n,i,max=0,c,d;
  double fb,fi,fa;
  scanf("%lld%lld%lld",&a,&b,&n);
  for(i=0;i<=n;i++){
    fb=(double)b;
    fa=(double)a;
    fi=(double)i;
    c=(long long int)(fa*fi/fb);
    d=i/b;
    if(max<c-a*d){
      max=c-a*d;
    }
  }
  printf("%lld\n",max);
  return 0;
}
