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备注:
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#include <iostream>
#include <cstdio>
#include <iomanip>
#include <cmath>
#include <math.h>
#include <algorithm>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <algorithm>
#define LL long long
using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 1e5 + 10;
double c , f;
int main()
{
	cin >> f;
    c = 5 * ( f - 32 ) / 9;
    cout << fixed << setprecision(5) << c;
	return 0;
}