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#include <bits/stdc++.h>
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using namespace std;
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int main() {
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    int count = 0, sum = 0;
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    while (true) {
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        int x;
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        cin >> x;
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        if (x == 0) {
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            break;
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        }
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        count++;
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        sum += x;
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    }
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    cout << fixed << setprecision(6) << double(sum) / count;
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    return 0;
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}