> # include <stdio.h>
> # include <string.h>
> 
> main(){
> 	int key,len,i,temp;
> 	char code[75],plain[75];
> 	while (scanf("%d",&key),key){
> 		scanf("%s",code);
> 		len=strlen(code);
> 		plain[len]=0;
> 		for (i=0;i<len;i++){
> 			switch (code[i]){
> 			case '_' :	temp=(1+i)%28;break;
> 			case '.' : 	temp=(27+i)%28;break;
> 			default	 :	temp=(code[i]-'a'+1+i)%28;
> 			}
> 			switch (temp){
> 			case 0  :	plain[(i*key)%len]='_';break;
> 			case 27 :	plain[(i*key)%len]='.';break;
> 			default :	plain[(i*key)%len]=temp+'a'-1;
> 			}
> 		}
> 		puts(plain);
> 	}
> }