Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	for scanner.Scan() {
		input := strings.Split(scanner.Text(), " ")
		ele_t1 := [3]int{}
		ele_t2 := [3]int{}
		for i := range ele_t1 {
			ele_t1[i], _ = strconv.Atoi(input[i])
			ele_t2[i], _ = strconv.Atoi(input[i+3])
		}
		if ele_t1[0] < 0 || ele_t1[1] < 0 || ele_t1[2] < 0 ||
			ele_t2[0] < 0 || ele_t2[1] < 0 || ele_t2[2] < 0 {
				break
		}
		t1 := time.Date(ele_t1[0], time.Month(ele_t1[1]), ele_t1[2], 0, 0, 0, 0, time.UTC)
		t2 := time.Date(ele_t2[0], time.Month(ele_t2[1]), ele_t2[2], 0, 0, 0, 0, time.UTC)
		diff := t2.Sub(t1)
		fmt.Printf("%v\n", int64(diff/(time.Hour*24)))
	}
}

C++: #include <iostream>

using namespace std;

int main() {
    int day[2][13] = { { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
    { 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 } };
    int y1, m1, d1, y2, m2, d2;
    while (cin >> y1 >> m1 >> d1 >> y2 >> m2 >> d2) {
        if (y1 < 0 || m1 < 0 || d1 < 0 || y2 < 0 || m2 < 0 || d2 < 0) {
            break;
        }
        int ans = 0;
        for (int i = y1, j = m1, k = d1; i <= y2; i++) {
            for (; j <= 12; j++) {
                for (; k <= day[(i % 4 == 0 && i % 100 != 0) || i % 400 == 0][j]; k++) {
                    if (i == y2 && j == m2 && k == d2) {
                        goto Fin;
                    }
                    ans++;
                }
                k = 1;
            }
            j = 1;
        }
    Fin:;
        cout << ans << endl;
    }
    return 0;
}

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

int y[2],m[2],d[2];

int t[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};

int calc(int y,int m,int d){
  int cnt=(y-1)/4-(y-1)/100+(y-1)/400;
  int res = y*365;
  res=res+cnt+1-365;


  if(y%4==0&&(y%100!=0||y%400==0))t[2]++;
  int cnt2=0;
  for(int i=1;i<=m;i++){
    for(int j=1;j<=(i==m?d-1:t[i]);j++){
      cnt2++;
    }
  }
  if(y%4==0&&(y%100!=0||y%400==0))t[2]--;

  return res+cnt2;
}


int main(){
  int a,b;
  while(cin>>y[0]>>m[0]>>d[0]>>y[1]>>m[1]>>d[1]){
    if(y[0]<0||m[0]<0||d[0]<0||y[1]<0||m[1]<0||d[1]<0)break;
    a=calc(y[0],m[0],d[0]);
    b=calc(y[1],m[1],d[1]);
    cout<<b-a<<endl;
  }

}

C++: #include<iostream>
using namespace std;
int x[1000000], day[13][32], day2[13][32], cnt, a, b, c, d, e, f, daya1, daya2;
int days[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };
int days2[13] = { 0,31,29,31,30,31,30,31,31,30,31,30,31 };
int main() {
	for (int i = 1; i < 1000000; i++) {
		if ((i % 4 == 0 && i % 100>0) || i % 400 == 0) {
			x[i] = x[i - 1] + 366;
		}
		else {
			x[i] = x[i - 1] + 365;
		}
	}
	for (int i = 1; i <= 12; i++) {
		for (int j = 1; j <= days[i]; j++) {
			day[i][j] = cnt;
			cnt++;
		}
	}
	cnt = 0;
	for (int i = 1; i <= 12; i++) {
		for (int j = 1; j <= days2[i]; j++) {
			day2[i][j] = cnt;
			cnt++;
		}
	}
	while (true) {
		cin >> a >> b >> c >> d >> e >> f;
		if (a < 0) { break; }
		if (b < 0) { break; }
		if (c < 0) { break; }
		if (d < 0) { break; }
		if (e < 0) { break; }
		if (f < 0) { break; }
		daya1 - 0; daya2 = 0;
		daya1 += x[a - 1];
		daya2 += x[d - 1];
		if (a % 4 == 1) {
			daya1 += day2[b][c];
		}
		else {
			daya1 += day[b][c];
		}
		if (d % 4 == 1) {
			daya2 += day2[e][f];
		}
		else {
			daya2 += day[e][f];
		}
		cout << daya2 - daya1 << endl;
	}
}

C++: #include <vector>
#include <list>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <cstdio>
#include <climits>
#include <complex>
#include <cstdint>
#include <tuple>

#define M_PI       3.14159265358979323846

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
inline int readInt() { int x; scanf("%d", &x); return x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,s,n) for(int i=s;i<(int)n;++i)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()

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

int N, K;
struct Edge {
    int to, cost;
    Edge(int to, int cost): to(to), cost(cost) {}
};

typedef vector<vector<Edge>> AdjList;
AdjList graph;

const int INF = 100000000;

vi dist;
int d[110][110];

bool bellman_ford(int n, int s) { // nは頂点数、sは開始頂点
    dist = vector<int>(n, INF);
    dist[s] = 0; // 開始点の距離は0
    for (int i = 0; i < n; i++) {
        for (int v = 0; v < n; v++) {
            for (int u = 0; u < n; u++) {
                if (dist[v] != INF && dist[u] > dist[v] + d[v][u]) {
                    dist[u] = dist[v] + d[v][u];
                    if (i == n - 1) return true; // n回目にも更新があるなら負の閉路が存在
                }
            }
        }
    }
    return false;
}
bool cmp(const pair<int,string>& a, const pair<int,string>& b){
    return a.first < b.first;
}

const int uruu = 366;

int days[13]={0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int main() {
    //cout << fixed << setprecision(15);

    
    int y1, m1, d1, y2, m2, d2;
    while(cin >> y1 >> m1 >> d1 >> y2 >> m2 >> d2){
        if(y1 <= -1 || m1 <= -1 || d1 <= -1 || y2 <= -1 || m2 <= -1 || d2 <= -1) break;
        
        LL ub=0, lb=0;
        
        for(int i = 1; i<=y1-1; ++i){
            if((i%4 == 0 && i%100 != 0) || i%400 == 0) lb += 366;
            else lb += 365;
        }
        
        if((y1%4 == 0 && y1%100 != 0) || y1%400 == 0) days[2]++;
        for(int i=1; i<m1; ++i){
            for(int j=1; j<=days[i]; ++j) lb++;
        }
        lb += d1;
        days[2] = 28;
        
        for(int i = 1; i<=y2-1; ++i){
            if((i%4 == 0 && i%100 != 0) || i%400 == 0) ub += 366;
            else ub += 365;
        }
        
        if((y2%4 == 0 && y2%100 != 0) || y2%400 == 0) days[2]++;
        for(int i=1; i<m2; ++i){
            for(int j=1; j<=days[i]; ++j) ub++;
        }
        ub += d2;
        cout << ub-lb << endl;
        
    }
    return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <queue>
#include <vector>
#include <sstream>

#define rep(x,to) for(int x=0;x<to;x++)
#define rep2(x,from,to) for(int x=from;x<to;x++)

using namespace std;

int f(int y,int m,int d){
	return (y*365+y/4-y/100+y/400+m*28+(m+1)*26/10+d-400);
}

int main(void){

  int d[6];
	while(!cin.eof()){
		rep(i,6) cin >> d[i];
		rep(i,6) if(d[i]<0) goto endd;
		
		if(d[1]<3){ d[1] +=12; d[0]--;}
		if(d[4]<3){ d[4] +=12; d[3]--;}
		cout << (f(d[3],d[4],d[5]) - f(d[0],d[1],d[2])) << endl;
	}
  endd:
	return 0;
	
}