ex3.c

#include <stdio.h>
#include <string.h>
#define NUM 100
int main(void)
{
char s1[NUM], s2[NUM], s3[NUM];

while(1){
	fgets(s1, NUM, stdin);
	fgets(s2, NUM, stdin);
	fgets(s3, NUM, stdin);
	
	if(s1[0]=='-' && s2[0]=='-' && s3[0]=='-'){
		break;
	}

	int sa = (s2[0] - s1[0] + 26) % 26;

	for(int i=0; i<strlen(s3)-1; i++){
		if(s3[i]==' '){
			printf(" ");
		}else{
			printf("%c", 'A' + (s3[i] - 'A' - sa + 26) % 26);
		}
	}
	printf("\n");
}

return 0;
}