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

int main(int argc, char* argv[]){
	long long A, B, N;
	scanf("%lld %lld %lld", &A, &B, &N);

	double v = 0.0;
	if(N<B){ v = (double) N/B; }
	else{ v = (double) (B-1)/B; }

	long long ans = (long long)floor( (double)A*v );
	printf("%lld\n", ans);

	return 0;

}