#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;
    }
  }*/
  i=b-1;
  if(i>n){
    i=n;
  }
  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;
}
