a="0123456789ABCDEF" d={} for i ,j in enumerate(a): d[j]=i def R_to_Ten(R,X): res=0 X=X[::-1] for i in range(len(X)): res+=d[X[i]]*R**i return res R,X=input().split() R=int(R) print(R_to_Ten(R,X))