#include <stdio.h>
#include <math.h>
int main(void){
  long long a,b,n,k,i;
  scanf("%lld %lld %lld",&a,&b,&n);
  k= floor((long double)a*n/b);
  if(b==1){
    printf("0");
    } else if(n<b) {
      printf("%lld",k);
    }else{
    k= floor((long double)a*(b-1)/b)-floor((long double)(b-1)/b);
          printf("%lld",k);
  }


  return 0;
}