X,a,r=1<<30;main(N,C,V){for(scanf("%d%d%d",&N,&C,&V);++X<=20;r=r<a?r:a)a=pow(N,1./X),a=(int)(X*(a-1)+(log(N)-X*log(a))/(log(a+1)-log(a))-1.e-9)*V+C*X;printf("%d\n",r+V);}