#include <stdio.h>
#include <math.h>
int main(void){
  long long a,b,n,k,i;
  scanf("%lld %lld %lld",&a,&b,&n);
  k= floor((long double)a*n/b);
    if(n<b) {
      printf("%lld",k);
      return 0;
    }else{
      for(i=n;i>=n-b;i--){
        if(i%b==b-1){
          k= floor((long double)a*(i)/b)-floor((long double)i/b);
          printf("%lld",k);
          return 0;
        }
      }
    }
}
