#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define rep(i,k,n) for(int (i)=(k);(i)<(n);(i)++)
#define max(a,b) (a)>(b)?(a):(b)
#define min(a,b) (a)<(b)?(a):(b)
#define abs(a,b) (a)< 0 ?(a):-(a)
#define llong long long

int next(int*,int,int);

int main(){
	llong A,B,N; scanf("%lld %lld %lld",&A,&B,&N);
	llong ans;
	if( N >= B ) ans = (A*(B-1))/B;
	else ans = (A*N)/B;
	printf("%lld",ans);
	return 0;
}
