#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
int main(void){
	long long A,B,N,ans,buff1,buff2,max;
	int i;
	char str[10000000],buf[10000000];
 
	fgets(str, sizeof(str), stdin);
	A=strtoll(strtok(str ," "),buf,10);
	B=strtoll(strtok(NULL," "),buf,10);
	N=strtoll(strtok(NULL," "),buf,10);

  max=0;
  
	for(i=0;i<=N;i++){
		buff1=A*i/B;
		buff2=i/B;
		buff2*=A;
		ans=buff1-buff2;
      	if(ans > max) max=ans;
	}
  
	printf("%ld\n",ans);

	return 0;
}