#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>

#include <sstream>
#include <algorithm>
#include <cmath>

#include <string>
#include <vector>
//#include <valarray>


#include <queue>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <list>

#include<cassert>//assert();
#include <fstream>
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
#ifdef getchar_unlocked
#define mygc(c) (c)=getchar_unlocked()
#else
#define mygc(c) (c)=getchar()
#endif
#ifdef putchar_unlocked
#define mypc(c) putchar_unlocked(c)
#else
#define mypc(c) putchar(c)
#endif
/////////
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
/////////
using namespace::std;
/////////
/////数値読み込み
#define ENABLE_READER_ON(T)	\
inline void reader(T &x){\
	int k;x = 0;bool flag = true;\
	while(true){\
		mygc(k);\
		if( k == '-'){\
			flag = false;break;\
		}\
		if('0' <= k && k <= '9'){\
			x = k - '0';break;\
		}\
	}\
	if( flag ){\
		while(true){\
			mygc(k);\
			if( k<'0' || '9'<k)break;\
			x = x * 10 + (k - '0');\
		}\
	}else{\
		while(true){\
			mygc(k);\
			if( k<'0' || '9'<k)break;\
			x = x * 10 - (k-'0');\
		}\
	}\
}
//整数
ENABLE_READER_ON(int)
ENABLE_READER_ON(long)
ENABLE_READER_ON(long long)
ENABLE_READER_ON(unsigned int)
ENABLE_READER_ON(unsigned long)
ENABLE_READER_ON(unsigned long long)

//////
//文字読み込み
inline int reader(char c[]){int i,s=0;
for(;;){mygc(i);if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF) break;}
c[s++]=i;
for(;;){mygc(i);if(i==' '||i=='\n'||i=='\r'||i=='\t'||i==EOF) break;c[s++]=i;}
c[s]='\0';return s;
}

inline int reader(string& c,int size=100){int i;c.reserve(size);
for(;;){mygc(i);if(i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF)break;}
c.push_back(i);
for(;;){mygc(i);if(i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF)break;c.push_back(i);}
return c.size();}

/////////
//小数はどうするのだろう
//
//数値出力
#define ENABLE_WRITER_ON(T)	\
inline void writer(T x){char f[20];int s = 0;\
if (x<0){mypc('-');while(x){f[s++] = ~(x%10)+1,x /= 10;}}\
else{while(x){f[s++] = (x % 10), x /= 10;}}\
if (!s)f[s++] = 0;while (s--)mypc(f[s] + '0');}

ENABLE_WRITER_ON(int)
ENABLE_WRITER_ON(long)
ENABLE_WRITER_ON(long long)
ENABLE_WRITER_ON(unsigned int)
ENABLE_WRITER_ON(unsigned long)
ENABLE_WRITER_ON(unsigned long long)
/////////
inline void writer(const char c[]){for (int i = 0; c[i] != '\0'; i++)mypc(c[i]); }
inline void writer(const string str){writer( str.c_str() );}
/////////
inline void solve(){
	int A;
	reader(A);
	if(A >= 15 ){
		writer(A-7);
	}else{
		writer(-1);
	}
	return;
	for(int i=0;i<=100;++i)
	{
		for(int j=8;j<=100;++j){
			if( i == j+7){
				cout << i << "\t" << j << endl;
				break;
			}
		}
	}
}

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//小数を10進数表示
    //cout << setprecision(16);//小数をいっぱい表示する。16?
	
	solve();
	return 0;
}