#include<stdio.h>
#include<math.h>
int main(){
   long a,b,n;
   scanf("%ld %ld %ld",&a,&b,&n);
   long x,ans;
   if(n>=b){
      x=b-1;
   }else{
      x=n;
   }
   ans = floor(a*x/b)-a*floor(x/b);
   printf("%ld\n",ans);
   return 0;
}
