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

#define ROT 13

int main(void) {

  char text[] = "bonjour agentty, ras de notre cote egalement. over", base;
  int i;

  for (i = 0; text[i] != '\0'; ++i) {
    if (isalpha(text[i])) {
      base = islower(text[i]) ? 'a' : 'A';
      text[i] = (text[i] - base + ROT) % 26 + base;
    }
  }

  printf("%s", text);

  return EXIT_SUCCESS;
}