Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextLineInt() []int {
	arr := strings.Split(nextLine(), " ")
	var ret []int
	for _, v := range arr {
		x, _ := strconv.Atoi(v)
		ret = append(ret, x)
	}
	return ret
}

func main() {
	cin := nextLineInt()
	F := cin[0]
	fmt.Println((F-30)/2)
}

C++: #include<iostream>
using namespace std;
int main (){
  int C,F;
  cin >> F ;
  C=(F-30)/2;
  cout << C << endl;
}

C++: #include <iostream>
using namespace std;
int main(void){
    int f;
    cin>>f;
    cout<<(f-30)/2<<endl;
}

C++: #include  <bits/stdc++.h>

using namespace std;

int main(){
    int x;
    
cin>>x;
cout<<(x - 30) / 2<<endl;

return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>	
#include<cmath>
using namespace std;
int main() {
	int n; cin >> n;
	cout << (n - 30) / 2 << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;

int main() {
  int f;
  cin >> f;
  cout << (f - 30) / 2 << "\n";
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
  long long n;
  cin >> n;
  cout << (n-30)/2 << endl;
  return 0;
}

C++: #include <iostream>

using namespace std;


int main() {
	
	int F;
	cin >> F;
	cout << (F - 30) / 2 << "\n";
	
	return 0;

}

C++: #include <iostream>
using namespace std;
int main(void){
    int F;
    cin >>F;
    
    cout << (F-30)/2 <<endl;
    
}

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

int main() {
  int F;
  cin >> F;
  cout << (F-30)/2 << endl;
  return 0;
}

C++: /*
　　　　 ∧＿∧　にっぽんちゃちゃちゃ
　／＼（　・∀・）／ヽ
（ ●　と　　　つ　● ）　にっぽんちゃちゃちゃ
　＼/⊂、 ノ　　＼ノ
　　　　　し'
*/
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define repone(i,n) for(int i=1;i<(int)(n);++i)
#define repo(i,o,n) for(int i=o;i<(int)(n);++i)
#define Rep(j,n) for(int j=0;j<(int)(n);++j)
#define Repo(j,o,n) for(int j=o;j<(int)(n);++j)
#define Repone(j,n) for(int j=1;j<(int)(n);++j)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define int long long
#define MOD 1000000007
#define INF 9223372036854775807

signed main()
{
int x=0,y=0,z=0,w=0,n=0,d=0;
std::cin >> x;
std::cout << (x-30)/2 << '\n';
}

C++: #include<iostream>
#include<iomanip>
#include<math.h>
#include<algorithm>
#include<functional>
#include<utility>
#include<queue>
#include<string.h>
#include<string>
#include<set>
#include<map>
#include<vector>
using namespace std;
typedef long long LL;
typedef pair<int, int> P;
LL N,M;

int main(){
    cin>>N;

    cout<<(N-30)/2<<endl;
    return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <math.h>
#include <algorithm>
using namespace std;
int main(){
  int a;
  cin >> a;
  cout << (a-30)/2 << endl;
}

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

int main(){
  int n;
  cin >> n;
  cout << (n-30)/2 << endl;
}

C++: #include<stdio.h>
int main(void)
{
	int a,x,y,z;
	scanf("%d",&a);
	x=a-30;
	y=x/2;
	printf("%d\n",y);
	return 0;
}

C++: # include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
typedef pair<LL, LL> pii;
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(ALL((wpwpw)));(wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)

int f;

int main(){
    INIT;
    cin >> f;
    cout << (f - 30)/2 << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
    int a;
    cin>>a;
    cout<<(a-30)/2<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
    int F;
    cin >> F;
    cout << (F - 30) / 2 << "\n";
    return 0;
}

C++: #include <iostream>
using namespace std;
int main(void){
  int f;
  cin>>f;
  cout<<(f-30)/2<<endl;
}

C++: #include <iostream>
using namespace std;
int main(void){
    // Your code here!
    int x;
    cin>>x;
    cout<<(x-30)/2<<endl;
}

C++: #include<iostream>
using namespace std;
int main(void){
	int F=0;
	cin>>F;
	cout<<(F-30)/2<<endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
int main(){int F;
    cin>>F;cout<<(F-30)/2<<endl;
    return 0;
}

C++: #include <iostream>
using namespace std;
int main(void){
    
    int F;
    cin>>F;
    cout<<(F-30)/2<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
    int a;
    cin >> a;
    cout << (a-30)/2 << endl;
}

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


  
int main(){
  

  int F;
  cin >>  F;
  cout  << (F-30)/2 << "\n";
 return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
    int f; cin >> f;
    cout << (f-30)/2 << endl;
}

C++: #include <bits/stdc++.h>
#include <cctype>
#include <cstring>
using namespace std;

int main(){
	int x;
	cin >> x;
	x = (x - 30) / 2;
	cout << x << endl;
}

C++: #include <iostream>
using namespace std;
int main(void){
    int f;
    cin>>f;
    cout<<(f-30)/2<<endl;
}

C++: #include<bits/stdc++.h>
using namespace std;
int main(){

  int F;
  cin>>F;

  cout<<(F-30)/2<<endl;
  return 0;
}

C++: #include<iostream>

using namespace std;
int main()
{
    int f;
    cin >> f;
    cout << (f-30)/2 << endl;
    return 0;
}

C++: #include<iostream>
#define REP(i,n) for(int i=0;i<n;i++)
#define INF 99999999

using namespace std;

int main(void){
	int f;
	cin >> f;
	cout << (f - 30) / 2 << endl;
	return 0;
}

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

int main(){
    int n;
    cin >> n;
    cout << (n-30)/2 << endl;
    return 0;
}

C++: #include"bits/stdc++.h"
using namespace std;


int main()
{
    int f;
    cin >> f;
    cout << (f-30)/2 << endl;
    return 0;
}

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

int main(){
    long int F,C;
    cin >> F;
    C=(F-30)/2;
    cout << C << '\n';

    return 0;

}

C++: #include <iostream>
using namespace std;
int main(void){
    int f;
    cin >> f;
    cout << (f-30)/2 << endl;
}

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

int main(){
  int F, C;
  cin>> F;

  C=(F-30)/2;

  cout<< C << endl;

  return 0;
}

C++: //PCK2018予選問題
#include "bits/stdc++.h"
using namespace std;
void math(int x){
    cout << (x-30)/2 << endl;
}

int main(){
  int f;
  cin >> f;
  
  math(f);

  return 0;
   
}

C++: #include<iostream>
using namespace std;
int F,C;
int main(){
cin>>F;
C=(F-30)/2;
cout<<C<<endl;
return 0;
}

C++: #include <iostream>
using namespace std;
int main(void){
    int f;
    cin>>f;
    cout<<(f-30)/2<<endl;
}

C++: #include<iostream>
#include<vector>
#include<cmath>
#define _GLIBCXX_DEBUG
using namespace std;

int main(){
  int F;
  cin>>F;
  cout<<(F-30)/2<<endl;
  return 0;
}

C++: #include <iostream>
using namespace std;
int main(){
    double a;
    cin >> a;
    cout << (a-30)/2 << endl;

    return 0;
}