#include <stdio.h>
int main(){
  long int a,b,c,ans=0;
  scanf("%ld%ld%ld",&a,&b,&c);
  if(c>=b-1){
    ans=a*(b-1);
    ans/=b;
  }
  else {
  ans=a*c;
  ans/=b;
  }
    
  printf("%ld",ans);
  return 0;
}