#include<stdio.h>
#define ull unsigned long long int
#define ll long long
#define rep(x) for(A[x]=A[x-1];A[x]<=M;A[x]++)

int main(){
  ll A,N,B;
  scanf("%lld%lld%lld",&A,&B,&N);
  if(N>=B)N=B-1;
  printf("%lld",A*N/B);
};