In Japan, temperature is usually expressed using the Celsius (℃) scale. In America, they used the Fahrenheit (℉) scale instead. $20$ degrees Celsius is roughly equal to $68$ degrees Fahrenheit. A phrase such as "Today’s temperature is $68$ degrees" is commonly encountered while you are in America.

A value in Fahrenheit can be converted to Celsius by first subtracting $32$ and then multiplying by $\frac{5}{9}$. A simplified method may be used to produce a rough estimate: first subtract $30$ and then divide by $2$. Using the latter method, $68$ Fahrenheit is converted to $19$ Centigrade, i.e., $\frac{(68-30)}{2}$.

Make a program to convert Fahrenheit to Celsius using the simplified method: $C = \frac{F - 30}{2}$.



Input

The input is given in the following format.


$F$


The input line provides a temperature in Fahrenheit $F$ ($30 \leq F \leq 100$), which is an integer divisible by $2$.

Output

Output the converted Celsius temperature in a line.

Examples

Input

68


Output

19


Input

50


Output

10
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vvll> vvvll;
typedef vector<string> vstr;
typedef pair<ll, ll> pll;
typedef vector<pll> vp;
typedef map<ll, ll> mll;
typedef map<string, ll> mstrll;
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fir first
#define sec second
#define maxs(x, y) (x = max(x, y))
#define mins(x, y) (x = min(x, y))
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define _overload3(_1, _2, _3, name, ...) name
#define _rep(i, n) repi(i, 0, n)
#define repi(i, a, b) for(ll i = ll(a); i < ll(b); i++)
#define rep(...) _overload3(__VA_ARGS__, repi, _rep,)(__VA_ARGS__)
#define each(i, n) for(auto&& i: n)
#define out(x) cout << (x)
#define indent() cout << '\n'
#define print(x) cout << (x) << '\n'
#define debug(x) cerr << #x << ": " << (x) << '\n'
ll gcd(ll a, ll b){return b != 0 ? gcd(b, a % b) : a;}
ll lcm(ll a, ll b){return a / gcd(a, b) * b;}
const ll INF = 1e16;
const ll MOD = 1e9 + 7;
ll a, b, c, n, m, x, y, z, w, h, ans, cnt, mx, mn;
string s, t;
ll dx[] = {-1, 0, 1, 0}, dy[] = {0, -1, 0, 1};
//vll dx = {-1, 0, 1, -1, 1, -1, 0, 1}, dy = {-1, -1, -1, 0, 0, 1, 1, 1};
string alphabet = "abcdefghijklmnopqrstuvwxyz";

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    while(cin >> n){
        print((n - 30)/ 2);
    }
}

