Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	for scanner.Scan() {
		var result string
		line := scanner.Text()
		key := make(map[string]string)

		var i int32
		for ; i < 52; i++ {
			makeKey(key, i)
			result = decode(key, line)

			if strings.Contains(result, "the") {
				break
			} else if strings.Contains(result, "this") {
				break
			} else if strings.Contains(result, "that") {
				break
			}
		}

		fmt.Println(result)
	}
}

func makeKey(key map[string]string, shift int32) {
	for i := 'a'; i <= 'z'; i++ {
		cipher := (i + shift)
		if cipher > 'z' {
			cipher = cipher%'z' + 'a' - 1
		} else if cipher < 'a' {
			cipher = cipher + ('z' - 'a') + 1
		}
		key[string(i)] = string(cipher)
	}
}

func decode(key map[string]string, cipher string) string {
	var result string
	for _, v := range cipher {
		if key[string(v)] != "" {
			result += key[string(v)]
		} else {
			result += string(v)
		}
	}
	return result
}

C++: // need
#include <iostream>
#include <algorithm>

// data structure
#include <bitset>
//#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
//#include <array>
//#include <tuple>
//#include <unordered_map>
//#include <unordered_set>
#include <complex>
//#include <deque>
#include<valarray>

// stream
//#include <istream>
//#include <sstream>
//#include <ostream>
#include <fstream>

// etc
#include <cassert>
#include <functional>
#include <iomanip>
//#include <typeinfo>
//#include <chrono>
#include <random>
#include <numeric>

#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest&...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int i=0; i<n; ++i){MACRO_VEC_ROW_Scan(i, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest&...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest&...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define OUT(d) std::cout<<d;
#define FOUT(n, d) std::cout<<std::fixed<<std::setprecision(n)<<d;
#define SOUT(n, c, d) std::cout<<std::setw(n)<<std::setfill(c)<<d;
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;
#define ALL(a) (a).begin(),(a).end()
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=(n)-1;i>=0;--i)
#define FORLL(i, a, b) for(ll i=ll(a);i<ll(b);++i)
#define RFORLL(i, a, b) for(ll i=ll(b)-1;i>=ll(a);--i)
#define REPLL(i, n) for(ll i=0;i<ll(n);++i)
#define RREPLL(i, n) for(ll i=ll(n)-1;i>=0;--i)
#define PAIR std::pair<int, int>
#define PAIRLL std::pair<ll, ll>
#define IN(a, x, b) (a<=x && x<b)
#define SHOW(d) {std::cerr << #d << "\t:" << d << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWPAIR(p) {std::cerr << #p << "\t:(" << p.first << ",\t" << p.second << ")\n";}
#define SHOWPAIRVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr<<'('<<yyy.first<<", "<<yyy.second<<") ";}std::cerr << "\n";}}
#define SHOWPAIRVECTOR(v) {for(const auto& xxx:v){std::cerr<<'('<<xxx.first<<", "<<xxx.second<<") ";}std::cerr<<"\n";}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t:";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
template<typename T> inline T CHMAX(T& a, const T b) { return a = (a < b) ? b : a; }
template<typename T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
#define EXCEPTION(msg) throw std::string("Exception : " msg " [ in ") + __func__ + " : " + std::to_string(__LINE__) + " lines ]"
#define TRY(cond, msg) try {if (cond) EXCEPTION(msg);}catch (std::string s) {std::cerr << s << std::endl;}
//void CHECKTIME(std::function<void()> f) { auto start = std::chrono::system_clock::now(); f(); auto end = std::chrono::system_clock::now(); auto res = std::chrono::duration_cast<std::chrono::nanoseconds>((end - start)).count(); std::cerr << "[Time:" << res << "ns  (" << res / (1.0e9) << "s)]\n"; }

#define int ll
using ll = long long;
using ull = unsigned long long;
constexpr int INFINT = 1 << 30;                          // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double EPS = 1e-7;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;

signed main() {
	INIT;
	std::string s;
	while (std::getline(std::cin, s)) {
		int t = 't' - s[0];
		for (char& c : s) {
			if (c == ' ' || c == '.') continue;
			c = ((c - 'a') + t + 26) % 26 + 'a';
		}
		OUT(s)BR;
	}
	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>


int main()
{
	char s[81];
	while (gets(s) != NULL)
	{
		for (int i = 0; i < 26; ++i)
		{
			char decoded[81];
			for (int j = 0; s[j] != '\0'; ++j)
				decoded[j] = islower(s[j]) ? 'a'+(s[j]-'a'+i)%26 : s[j];
			decoded[strlen(s)] = '\0';
			if (strstr(decoded, "the")
				|| strstr(decoded, "this")
				|| strstr(decoded, "that"))
			{
				puts(decoded);
				break;
			}
		}
	}
	return 0;
}

C++: #include <iostream>

char sub(char a, char b) {
	if (a < b) return (26 + a - b);
	return (a - b);
}

char add(char a, char offset) {
	return ((((a - 'a') + offset) % 26) + 'a');
}

int main() {
	char offset;
	int num;
	std::string str;
	while (getline(std::cin, str)) {
		offset = 0;
		num = 0;
		for (int i=0; i<str.length(); i++) {
			if ('a' <= str[i] && str[i] <= 'z') {
				num++;
				if (i < str.length() - 1) {
					continue;
				}
				i++;
			}
			if ((num == 3
			&& sub(str[i-3], str[i-2]) == 12
			&& sub(str[i-3], str[i-1]) == 15)
			|| (num == 4
			&& sub(str[i-4], str[i-3]) == 12
			&& sub(str[i-4], str[i-2]) == 11
			&& sub(str[i-4], str[i-1]) == 1)
			|| (num == 4
			&& sub(str[i-4], str[i-3]) == 12
			&& sub(str[i-4], str[i-2]) == 19
			&& sub(str[i-4], str[i-1]) == 0))
			{
				offset = sub(str[i-num], 't');
				break;
			}
			num = 0;
		}
		for (int i=0; i<str.length(); i++) {
			if ('a' <= str[i] && str[i] <= 'z') {
				str[i] = add(str[i], 26 - offset);
			}
		}
		std::cout << str << std::endl;
	}
	return 0;
}

C++: 
#include <stdio.h>
#include<string.h>
int main()
{
    char a[200];
    int i,b,x,l,c,in;
    while(gets(a)!=EOF)
    {
        l=strlen(a);
         b=(int)a[0];
         x=116-b;
        for(i=0;i<l;i++)
        {
            if(a[i]>=97&&a[i]<=122)
            {
                in=(int)a[i];
                a[i]=in+x;
                }
            printf("%c",a[i]);
        }
        printf("\n");}
        return 0;

}