#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define MP(a,b) make_pair(a,b)
int main() {
	ios::sync_with_stdio ( false );
	double F;
	cin >> F;
	cout << fixed << setprecision ( 5 ) << 5 * ( F - 32 ) / 9 << endl;
	return 0;
}