#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

int main (int argc, string argv[]){
    // testing if user has put correct number of arguments in command-line
    if (argc != 2){
        return 1;
    }
    
    // transforming the string containing the key into an actual integer
    int k = atoi(argv[1]);
    
    //getting the plain text from the user
    string  plaintext = GetString();
   
    //declaring the string that will contain the cypher text
    string cipher[strlen(plaintext)];
    
    int letter;
    
    for (int i=0, j= strlen(plaintext); i<j; i++)
    { 
       // getting letter to be changed 
       letter = (int) plaintext[i];
       // checking if character is actually alphabetic
       if (isalpha(plaintext[i])){
              
           letter = (letter) + (k% 26);
           // checking if wrap round  from Z to A is needed
           if (isupper(plaintext[i])){
               if (letter>90){ 
                   letter= 65+ letter-91; 
               }
           }
           if (islower(plaintext[i])){
           // checking if wrap round  from z to a is needed
               if (letter>122){ 
                   letter= 97+ letter-123; 
               }
           }
           cipher[i]= (string) letter;
           printf("%c", (char) cipher[i]);
       }
       else{
           printf("%c", (plaintext[i]));
       }
       
    }
    printf("\n");
    return 0;
}