K = 7

ZeroJudge Link (Zh)

#include <stdio.h>

main() {
  char str[100];
  while(scanf("%s", str) != EOF) {
    int i = 0;
    while(str[i]) {
      str[i++] -=7;
    }
    printf("%s\n", str);
  }
  return 0;
}