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

int main(int argc, char ** argv){
	if(argc < 2){
		printf("Usage:  %s shift [-d]\n", argv[0]);
		return 1;
	}
	char decrypt = 0;
	if(argc > 2 && argv[2][1] == 'd')
		decrypt = 1;
	unsigned int shift = atoi(argv[1]); // actually puts the sift in an int, might break shifts >2^31
	unsigned int buffer[256];
	size_t len; 
	while(len = read(0, buffer, sizeof(buffer))){
		for(int i = 0; i < len/sizeof(int); i++){
			if(decrypt)
				buffer[i] -= shift;
			else
				buffer[i] += shift;
		}
		write(1, buffer, len);
	}
	return 0;
}