#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define max(a,b) ((a)>(b)?(a):(b))

int main(){
	long long int i,n,a,b,ans=-1;
	scanf("%lld %lld %lld",&a,&b,&n);
	for(i=0;i<=n;i++){
		ans=max(ans,floor(i*a/b)-a*floor(i/b));
	}
	printf("%lld",ans);
	return 0;
}