Go: package main

// import (
// 	"fmt"
// 	"bufio"
// 	"strconv"
// 	"os"
// )

// func fib(n int) int{
// 	if n == 0 || n == 1{
// 		return 1
// 	} else {
// 		return fib(n-1) + fib(n-2)
// 	}
// }

// func main(){
// 	sc := bufio.NewScanner(os.Stdin)
// 	sc.Scan()
// 	n, _ := strconv.Atoi(sc.Text())
// 	fmt.Println(fib(n))
// }

import (
	"fmt"
)

func main(){
	var n, pre1, pre2, now int
	fmt.Scan(&n)
	if n == 0 || n == 1{
		fmt.Println(1)
	} else {
		pre1, pre2 = 1, 1
		for i:=1; i<n; i++{
			now = pre1 + pre2
			pre2 = pre1
			pre1 = now
		}
		fmt.Println(now)
	}

}

C++: #include <iostream>
#include <algorithm> // next_permutation
#include <iomanip>
#include <cmath>
#include <vector>
#include <sstream>
#include <string>
#include <cstdio>
#include <stack>
#include <queue>
#include <list>
#include <numeric> //accumulate
//#include <unordered_map> //???????????\??¢??°
#include <fstream> //ifstream, ofstream

//#define NDEBUG //NDEBUG???#include <cassert>???????????????????????????????????´???assert?????????????????????????????????NDEBUG?????????????????????????????????????????????
#include <cassert> //assert


using namespace std;

//???????????°??????TEST????????????????????¬???????????????????????????????????¢????????????
#define TEST //*******************************************************************************************************************************************
//?????????????????¨??§?????\????????????????????????????????°?????????????¨???????????????????dout???????????????????????§???????????¬??????????????????????????????????????????
//??????????????????????????????????????????????????????????§?CPU???????£??????????????????§???TLE?????????????????????????????????????????§????????¨???                           ????????????????????????cerr????????£????????????????????????????????????
#ifdef TEST
#define dout cout
#define din cin
#else
stringstream dummy; //???????????°??????dout?????????????????????????????????
#define dout dummy.str(""); dummy.clear(stringstream::goodbit); dummy //dummy?????????????????????????????????????????¨?????¢?????¢???????????????
//???????????¨??????????????????goodbit?????????????????????????????¨???????????´????????????????????????????????¨?????°?????????????????§???????????????????????????????????? http://d.hatena.ne.jp/linden/20060427/p1
#endif

//?¨??????????????????????????????????????????????????????´??????OUTPUTFILE????????????????????¬???????????????????????????????????¢????????????
//#define OUTPUTFILE "output.txt" //*******************************************************************************************************************************************
#ifdef OUTPUTFILE
#define dout outputfile //??¨????????????TLE????????§?????????dout?????¨??¨??????????????¢????????????????????????????????????????????§????¨????????????´??????????????£??????????????????????¨?????????????????????????????????????????????§?????????????????????
ofstream outputfile(OUTPUTFILE);
#define OutputFilePath "/Users/Nag/Documents/Prgm/Test/DerivedData/Test/Build/Products/Debug/output.txt"
#endif

//?¨??????\???????????????????????????????????????????????´??????INPUTFROMTEXTFILE????????????????????¬???????????????????????????????????¢????????????
//#define INPUTFILE "input.txt" //*******************************************************************************************************************************************
#ifdef INPUTFILE
#define din inputfile
ifstream inputfile(INPUTFILE);
#endif


#define disp(A) dout << #A << " = " << (A) << endl
#define disP(A) dout << setw(3) << (A) << " " // << setw(3) ??????????????\????????????
#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)

#define dispAll(A,n) dout << #A << " = "; rep(j, 0, (n)) {disP(A[j]);} dout << endl

typedef pair<int,int> pii;
typedef vector<int> vi;
typedef unsigned long long ll;

const int INF = 1e9-1;

int F[45] = {0};

int fibonacci(int n) {
    if(F[n]!=0) return F[n];
    
    if(n==0 || n==1) return F[n]=1;
    
    return F[n] = (fibonacci(n-1) + fibonacci(n-2));
}


int main() {
    
//    dout << fibonacci(n) << endl;
    
    rep(i,0,45) {
        if(i==0 || i==1) F[i] = 1;
        else F[i] = F[i-1]+F[i-2];
    }
    
    int n; cin >> n;
    
    dout << F[n] << endl;
    
    
#ifdef INPUTFILE
    inputfile.close();
#endif
    
#ifdef OUTPUTFILE
    outputfile.close();
    cout << "\"" << OutputFilePath << "\"" << endl;
#endif
    
    return 0;
}

C++: #include <iostream>
using namespace std;
int num;


int fib(int n, int array[]) {
    array[0] = 1;
    array[1] = 1;
    for (int i= 2; i <= n; i++) {
        array[i] = array[i - 1] + array[i - 2];
    }
    cout << array[n] << endl;
}
int main(void) {

    cin >> num;
    int array[num] = {};
    fib(num, array);


}

C++: #include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>
#include <algorithm>
#include <complex>
#include <array>
#include <iomanip>
using namespace std;

#define REP(i,n) for(int i=0; i<n; ++i)
#define FOR(i,a,b) for(int i=a; i<=b; ++i)
#define FORR(i,a,b) for (int i=a; i>=b; --i)
#define ALL(c) (c).begin(), (c).end()

typedef long long ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<long double> VD;
typedef vector<VI> VVI;
typedef vector<VL> VVL;
typedef vector<VD> VVD;
typedef pair<int,int> P;
typedef pair<ll,ll> PL;

template<typename T> void chmin(T &a, T b) { if (a > b) a = b; }
template<typename T> void chmax(T &a, T b) { if (a < b) a = b; }

int in() { int x; scanf("%d", &x); return x; }
ll lin() { ll x; scanf("%lld", &x); return x; }
#define INF 1LL<<60

int main() {
    int N;
    cin >> N;
    vector<int> dp(N+1);
    dp[0] = 1;
    dp[1] = 1;
    FOR(i, 2, N) {
        dp[i] = dp[i-1] + dp[i-2];
    }
    cout << dp[N] << endl;
    return 0;
}

C++: #include<stdio.h>
#define N 45

int F[N];

int fibonacci(int n)
{
    if(n==0 || n==1){
        F[n]=1;
        return F[n];
    }
    else if(n<N){
        F[n]=fibonacci(n-2)+fibonacci(n-1);
    return F[n];
    }
    return F[n];
}

int main(){
    int n;
    scanf("%d",&n);
    printf("%d\n",fibonacci(n));
    return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i,n) for(int (i) = 0;(i) < (n);(i)++)
#define SORT(c) sort((c).begin(),(c).end())
#define MOD 1000000007 //S.size() 配列名.Length()
using namespace std;
typedef unsigned long long ll;

ll memo[100];

/*ll func(ll n){
	if(memo[n] != -1)return memo[n];

	if(n == 0) return memo[n] = 1;
	else if(n == 1) return memo[n] = 1;
	else return memo[n] = func(n - 1) + func(n - 2);
}*/

ll func(ll n){
	memo[0] = 1;
	memo[1] = 1;
	for(int i = 2; i <= n; i++){
		memo[i] = memo[i - 1] + memo[i - 2];
	}
	return memo[n];
}

int main(void){
	//rep(i, 100) memo[i] = -1;
	ll n;
	cin >> n;
	cout << func(n) <<endl;

}

C++: #include <iostream>
#include <list>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <algorithm>
#include <cmath>
#include <string>
using namespace std;
typedef long long lli;
typedef vector<lli> vll;
typedef vector<bool> vbl;
typedef vector<vector<lli> > mat;
typedef vector<vector<bool> > matb;
typedef vector<string> vst;
typedef pair<lli,lli> pll;
typedef pair<double,double> pdd;

vll dp;

lli fib(lli x){
    if(dp[x]) return dp[x];
    if(x == 0) return dp[x] = 1;
    if(x == 1) return dp[x] = 1;
    return dp[x] = fib(x-1) + fib(x-2);
}

lli n;

int main(){
    cin >> n;
    dp = vll(n+1);
    cout << fib(n) << endl;
    return 0;
}