#include<stdio.h>

int main(){
  long int x = 0;
	double A, B, N;
	scanf("%lf %lf %lf", &A, &B, &N);
	if(N > B){
      x = A * ((B - 1) / B);
		printf("%ld", x);
	}
	else{
      x = A * (N / B);
		printf("%ld", x);
	}

	return 0;
}