#include <stdio.h>

int main(void){
  unsigned long long a,b,n;
  scanf("%lld %lld %lld",&a,&b,&n);
   
  if(b-1>n){
    printf("%lld\n",(a*n)/b);
  }
  else{
    printf("%lld\n",(a*(b-1))/b);
  }
  
  return 0;
}