#include<stdio.h>

int main(void){
    int a;
	unsigned long int b,n;
	unsigned long int x;
	unsigned long int flr1,flr2;
    unsigned long int tmp=0;
	
    scanf("%d %lu %lu",&a,&b,&n  );
		for(x=1;x<=n;x++){
			flr1=a*x / b;
			flr2= x / b;
			if(tmp <= flr1 - a*flr2){
				tmp= flr1 - a*flr2 ;
			}
		}
		printf("%lu",tmp);
	}