#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#define F(i,a,n) for(int i=a; i<n; i++)
#define INF 100000000000 // long only


int main(){
  long a,b,n;
  scanf("%ld%ld%ld",&a,&b,&n);
  double y=((double)b-1)/(double)b;
  if(b-1>n){
    double x=(double)n/(double)b;
    x=x-floor(x);
    printf("%ld",(long)((double)a*x));
    return 0;
  }
  double x=y-(long)y;
  printf("%ld\n",(long)((double)a*x));
  
  return 0;
}