#include <stdio.h>
 
int main()
{
    unsigned long long int a,b,n;
    scanf("%llu %llu %llu",&a, &b,&n);
    unsigned long long int max=0;
    unsigned long long int ans=0;
for(int i = 0;i<=n;i++){
ans=((i*a)/b)-a*(i/b);
if(ans>max){
    max=ans;
}
}
     printf("%llu",max);
    return 0;
}