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>
#include <fstream>
#include <string> 
#include <cstring>
#include <cmath>  
#include <cstdlib>
#include <ctime>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <deque>
#include <functional>
#include <cctype>
#include <list>
//#include <boost/multiprecision/cpp_int.hpp>

#define BIT(a) (1 << (a))
#define EPS (1e-10)

using namespace std;
//using namespace boost::multiprecision;

const long long MOD = 1000000007;
const int COUNTER_CLOCKWISE = 1;
const int CLOCKWISE = -1;
const int ONLINE_BACK = 2;
const int ONLINE_FRONT = -2;
const int ON_SEGMENT = 0;

class Point{
    public:
    double x, y;

    Point(double x = 0, double y = 0): x(x), y(y) {}
    
    Point operator+(Point p){return Point(x + p.x, y + p.y);}
    Point operator-(Point p){return Point(x - p.x, y - p.y);}
    Point operator*(double a){return Point(a * x, a * y);}
    Point operator/(double a){return Point(x / a, y / a);}

    bool operator < (const Point &p) const {
        return y != p.y ? y < p.y : x < p.x;
    }

    double norm(){return x * x + y * y;}
};
typedef Point Vector;
typedef vector<Vector> Polygon;

double cross(Vector a, Vector b){
    return a.x*b.y - a.y*b.x;
}

double dot(Vector a, Vector b){
    return a.x * b.x + a.y * b.y;
}

int ccw(Point p0, Point p1, Point p2){
    Vector a = p1 - p0;
    Vector b = p2 - p0;
    if (cross(a, b) > EPS)return COUNTER_CLOCKWISE;
    if (cross(a, b) > -EPS)return CLOCKWISE;
    if (dot(a, b) < -EPS)return ONLINE_BACK;
    if (a.norm() < b.norm())return ONLINE_FRONT;

    return ON_SEGMENT;
}

Polygon andrewScan(Polygon s){
    Polygon u, l;
    if (s.size() < 3) return s;
    sort(s.begin(), s.end());
    u.push_back(s[0]);
    u.push_back(s[1]);
    l.push_back(s[s.size()-1]);
    l.push_back(s[s.size()-2]);
    
    for (size_t i = 2; i < s.size(); i++){
        for (size_t n = u.size(); n >= 2 && ccw(u[n-2], u[n-1], s[i]) == COUNTER_CLOCKWISE; n--){
            u.pop_back();
        }
        u.push_back(s[i]);
    }

    for (int i = (int)s.size() - 3; i >= 0; i--){
        for (size_t n = l.size(); n >= 2 && ccw(l[n-2], l[n-1], s[i]) == COUNTER_CLOCKWISE; n--){
            l.pop_back();
        }
        l.push_back(s[i]);
    }

    reverse(l.begin(), l.end());
    for (size_t i = u.size() - 2; i >= 1; i--) l.push_back(u[i]);

    return l;
}

long long mod_pow(long long x, long long n){
    long long res = 1;
    for(int i = 0;i < 60; i++){
        if(n >> i & 1) res = res * x % MOD;
        x = x * x % MOD;
    }
    return res;
}


int ly[51];
int ry[51];
int lm[51];
int rm[51];
int ld[51];
int rd[51];

int mimos[13];

int  init(){
    int month[14] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    for (int i = 1; i < 13; i++){
        mimos[i] = month[i] + mimos[i-1];
    }
    return 0;
}


int main(void){
    int cnt = 0;
    init();
    while (1){
        int tmp[6];
        int flag = 0;
        for (int i = 0; i < 6; i++){
            cin >> tmp[i];
            if (tmp[i] == -1) flag = 1;
        }
        if (flag) break;
        ly[cnt] = tmp[0];
        lm[cnt] = tmp[1];
        ld[cnt] = tmp[2];
        ry[cnt] = tmp[3];
        rm[cnt] = tmp[4];
        rd[cnt] = tmp[5];
        cnt++;
    }

    for (int i = 0; i < cnt; i++){
        long long ans = 0;
        ans += (ry[i] - ly[i])*365;
        ans += (mimos[rm[i]] - mimos[lm[i]] - ld[i] + rd[i]);
        if (!ly[i] % 4){
            if (lm[i] > 4 ){
                ans++;
                if (!ly[i] % 100){
                    ans--;
                    if (!ly[i] % 400){
                        ans++;
                    }
                }
            }
        }
        
        for (int j = ly[i]; j < ry[i]; j++){
            if (j % 4 == 0){
                ans += ((ry[i] - j - 1) / 4) + 1;
                break;
            }
        }

        for (int j = ly[i]; j < ry[i]; j++){
            if (j % 100 == 0){
                ans -= (((ry[i] - 1 - j) / 100) + 1);
                break;
            }
        }

        for (int j = ly[i]; j < ry[i]; j++){
            if (j % 400 == 0){
                ans += (((ry[i] - 1 - j) / 400) + 1);
                break;
            }
        }

        cout << ans << endl;
    }
    return 0;
}

C++: #include <iostream>
using namespace std;
#define rep2(x,from,to) for(int x=(from);x<(to);++(x))
#define rep(x,to) rep2(x,0,to)
int d[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int calc(int y1, int y2) {
	int a;
	a = y2/4 - y1/4;
	if(y2%4==0 || y1%4==0) a++;
	a -= y2/100 - y1/100;
	if(y2%100==0 || y1%100==0) a--;
	a += y2/400 - y1/400;
	if(y2%400==0 || y1%400==0) a++;
	return a;
}
bool uruu(int y) {
	return y%4 == 0 && y%100 != 0 || y%400 == 0;  
}
int main() {
	int y1, m1, d1, y2, m2, d2;
	while(cin >> y1 >> m1 >> d1 >> y2 >> m2 >> d2 && (y1>=0 && m1>0 && d1>0 && y2>=0 && m2>0 && d2>0)) {
		int uy = calc(y1,y2);
		int ret = (y2-y1+1)*365+uy;
		int day = 0;
		rep(i,m1-1) day += d[i];
		for(int i=11; i>=m2; --i) day += d[i];
		day += d1-1, day += d[m2-1]-d2+1;
		if(uruu(y2) && m2>2) day++;
		cout << ret - day << endl;
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
int Q(int y,int m,int d) {
  if (m==1||m==2){--y;m+=12;}
   return 365*y+y/4-y/100+y/400+(306*(m+1))/10+d-428;
}
int main(){
  int a,b,c,d,e,f,g;
  while(cin>>a>>b>>c>>d>>e>>f){
    if(a<0)break;
    cout<<Q(d,e,f)-Q(a,b,c)<<endl;
  }
}

C++: #include<stdio.h>
int main(void){
   int y1, m1, d1, y2, m2, d2, Y1, Y2;
   while {
       scanf("%d %d %d %d %d %d", &y1, &m1, &d1, &y2, &m2, &d2);
       /*???????????´????±????????????????*/
       if ( m1 >= 3) Y1 = y1 + 1;
       else Y1 = y1;
       if ( m2 >= 3 ) Y2 = y2;
       else Y2 = y2 - 1;
       /*???????????´?????°????±???????*/
       for ( i = Y1; i < Y2; i++ ) {
           if ( i % 4 == 0 ) {
               if ( i % 400 == 0 ) u++;
               else if ( i % 100 == 0 ) u++;
               else u++;
           }
       }

    }
   return 0;
}

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

int main(){
  int i,j,y[2],m[2],d[2],ans,f;
  while(1){
    f = 0;
    for(i=0;i<2;i++){
      cin >> y[i] >> m[i] >> d[i];
      if(y[i] == -1 || m[i] == -1 || d[i] == -1) f++;
    }
    if(f != 0) break;

    ans = (y[1] - y[0]) * 365 + (m[1] - m[0]) * 30 + d[1] - d[0];

    for(i=m[0];i<=m[1];i++){
      if((i == 1 || i == 3 || i == 5 || i == 7 || i == 8 || i == 10 || i == 12) && i != m[1]) ans++;
    }

    for(i=y[0];i<=y[1];i++){
      if(i%4 == 0 && (i != y[1] || m[1] > 2)){
	if(i%400 == 0);
	else if(i%100 == 0) continue;
	if(i == y[0] && m[0] > 2) continue;
	ans++;
      }
    }

    cout << ans << endl;

  }
  return 0;
}