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

int main(){
  int a,b,n;
  int temp,ans = 0;
  scanf("%d %d %d",&a,&b,&n);
  
  for( int x = n ; x > 0 ; x--){
    temp = floor( ( a * x ) / b ) - a * floor( x / b );
    if(temp > ans){
      ans = temp;
    }
    if( x < b )break;
  }
  printf("%d\n",ans);
}