void reverse(char* str, int begin, int end)

 {

     char temp;

     for( ; begin < end; begin++)

     {

         temp = str[end];

         str[end] = str[begin];

         str[begin] = temp;

     }

 }

 void left_shift(char *str, int n, int k)

 {

     k=k% N;

     reverse(str, , k -);

     reverse(str, k , n - );

     reverse(str, , n - );

 }