不過估計數據量很大，竟然是16ms
#include <stdio.h>
#include <stdlib.h>

int main() {
	char c;
	bool first = 1;
	while(1){
		c = getchar();
		if(c == EOF) return 0;
		if(c != '"') printf("%c", c);
		else if(first){
			printf("``");
			first = 0;
		}
		else{
			printf("''");
			first = 1;
		}
	}
	return 0;
}