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 <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;
	}
}

C++: #include<iostream>

using namespace std;

bool isLeap(int y)
{
	if(y%400==0)	return true;
	if(y%100==0)	return false;
	if(y%4==0)		return true;
	return false;
}

int NumberOfDays(int y,int m,int d)
{
	int num=0;
	int mon[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
	if(isLeap(y))	mon[2]++;

	for(int i=1;i<y;i++)	num+=isLeap(i)?366:365;
	for(int i=1;i<m;i++)	num+=mon[i];
	num+=d-1;

	return num;
}

int main()
{
	int y1,m1,d1,y2,m2,d2;
	while(cin>>y1>>m1>>d1>>y2>>m2>>d2){
		if(!(~y1&&~m1&&~d1&&~y2&&~m2&&~d2))	break;
		cout<<NumberOfDays(y2,m2,d2)-NumberOfDays(y1,m1,d1)<<endl;
	}
	return 0;
}

C++: #include <iostream>
using namespace std;int main(){int a,b,c,d,e,f,g;int h[13]={0,0,31,59,90,120,151,181,212,243,273,304,334};while(1){cin>>a>>b>>c>>d>>e>>f;if(y==-1)break;g=f-c+h[mm]-h[m]+(d-a)*365;if(e<3)d--;if(b<3)a--;g+=d/4-a/4-d/100+a/100+d/400-a/400;cout<<g<<endl;}return 0;}

C++: 
#include<iostream>
using namespace std;
#define REP(i,b,n) for(int i=b;i<n;i++)
#define rep(i,n)   REP(i,0,n)

int month[]={
  0,
  31,//1
  28,//2
  31,//3
  30,//4
  31,//5
  30,//6
  31,//7
  31,//8
  30,//9
  31,//10
  30,//11
  31//12
};

int day(int y,int m,int d){
  int base = d;
  REP(i,1,m)base+=month[i];
  int lim = m > 2 ? y+1:y;
  REP(i,1,y)base+=365;
  REP(i,0,y){
    if ( i %400 == 0 ||
	 (i % 100 !=0 && i % 4 == 0))base++;
  }
  return base;
}



/*
  correct version

int day2(int y,int m,int d){
  y += 4800;
  if (m < 3) --y, m += 12;
  return 365L*y+y/4-y/100+y/400+(153*m-457)/5+d-32045;
}
*/

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;
    int a=day(y1,m1,d1),b=day(y2,m2,d2);
    //cout << day(y1,m1,d1)<<" " << day2(y1,m1,d1)<<" " << 
    //  day(y2,m2,d2)<<" " << day2(y2,m2,d2) << endl;
    
    cout << b-a << endl;
  }
}