Go: package main

import (
	"bufio"
		"os"
	"strings"
	"strconv"
		"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)))
		fmt.Println(ut2jd(ele_t2[0], ele_t2[1], ele_t2[2])-ut2jd(ele_t1[0], ele_t1[1], ele_t1[2]))
	}
}

func ut2jd(year, month, day int) int {
	if month <= 2 {
		year--
		month += 12
	}
	s := 3 + year/4 - year/100 + year/400
	s += 1720994 + year*365 + (month+1)*30 + (month+1)*3/5 + day
	return s
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

bool leap(int y)
{
	if(y % 400 == 0)
	{
		return true;
	}
	else if(y % 100 != 0 && y % 4 == 0)
	{
		return true;
	}
	return false;
}

int main()
{
	int days[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
	int days_leap[13] = {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 sum = 0;

		if(y2 - y1 == 0)
		{
			if(m2 - m1 == 0)
			{
				sum += d2 - d1;
			}
			else
			{
				if(leap(y1))
				{
					sum += days_leap[m1] - d1;
					
					REP(i,m1+1,m2)
					{
						sum += days_leap[i];
					}
					
					sum += d2;
				}
				else
				{
					sum += days[m1] - d1;

					REP(i,m1+1,m2)
					{
						sum += days[i];
					}

					sum += d2;
				}
			}
		}
		else
		{
			if(leap(y1))
			{
				sum += days_leap[m1] - d1;
				
				REP(i,m1+1,13)
				{
					sum += days_leap[i];
				}

			}
			else
			{
				sum += days[m1] - d1;

				REP(i,m1+1,13)
				{
					sum += days[i];
				}
			
			}

			REP(i,y1+1,y2)
			{
				if(leap(i))
				{
					sum += 366;
				}
				else
				{
					sum += 365;
				}
			}

			if(leap(y2))
			{
				REP(i,1,m2)
				{
					sum += days_leap[i];
				}
				sum += d2;
			}
			else
			{
				REP(i,1,m2)
				{
					sum += days[i];
				}
				sum += d2;
			}

		}

		cout << sum << endl;
	}
	return 0;
}

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){
            int d;
            if(i == m1) d = d1;
            else d = days[i];
            for(int j=1; j<= d; ++j) lb++;
        }
        
        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){
            int d;
            if(i == m2) d = d2;
            else d = days[i];
            for(int j=1; j<= d; ++j) ub++;
        }
        cout << ub-lb << endl;
        
    }
    return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstring>
#include <climits>
using namespace std;
static const double EPS = 1e-5;
typedef long long ll;

int uru(int y){
	return y%4==0 && (y%100!=0 || y%400==0);
}

int day(int y,int m,int d){
	int days=0;
	for(int i=1;i<=y-1;i++)days+=uru(i)+365;
	
	if(m>1)days+=31;
	if(m>2)days+=28+uru(y);
	if(m>3)days+=31;
	if(m>4)days+=30;
	if(m>5)days+=31;
	if(m>6)days+=30;
	if(m>7)days+=31;
	if(m>8)days+=30;
	if(m>9)days+=30;
	if(m>10)days+=31;
	if(m>11)days+=30;
	
	days+=d-1;
	return days;
}

main(){
	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;
		
		cout<<day(y2,m2,d2)-day(y1,m1,d1)<<endl;
	}
}