#include <stdio.h>
#define max(a, b) ((a)<(b) ? (b) : (a))

int main(){
  long long int a, b, n;
  scanf("%lld%lld%lld", &a, &b, &n);

  int score = 0;

  if(n <= b*2){
    for(long long int i=1; i<=n; i++){
      score = max(score, (long long int)(a*i/b)-a*(long long int)(i/b));
    }
  }else{
    for(long long int i=b-1; i<=n; i+=b){
      //      score = max(score, (long long int)(a*i/b)-a*(long long int)(i/b));
      if((long long int)(a*i/b)-a*(long long int)(i/b) < score){
	break;
      }
      score = max(score, (long long int)(a*i/b)-a*(long long int)(i/b));
    }
  }

  printf("%d\n", score);
  return 0;
}
