题解

#include <bits/stdc++.h>
using namespace std;
long long k , aa , bb;
string a,b;
long long modd ( long long a, long long b ) {
	if (b==0) return 1;
	if (b%2==1) return a * modd ( a , b-  1 ) ;
	else return modd ( a , b / 2 ) * modd ( a , b / 2 ) ;
}
int main ( ) {
    int t = 0;
    cin >> k >> a >> b;
    for ( int i = a . size() - 1 ; i >= 0; i-- ) {
        aa += ( a [ i ] - '0' ) * modd ( k , t++ ) ;
    }
    t = 0 ;
    for ( int i = b . size() - 1 ; i >= 0 ; i-- ) {
        bb += ( b [ i ] - '0' ) * modd ( k , t ++ ) ;
    }
    cout<<aa * bb;
}