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15 lines
251 B
C++
15 lines
251 B
C++
#include <bits/stdc++.h>
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using namespace std;
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int main() {
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int n, m, v, a, ans = 0;
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cin >> n >> v >> m >> a;
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for (int i = 1; i <= n; i++) {
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ans += v;
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if (i % m == 0) v += a;
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}
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cout << ans << endl;
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return 0;
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}
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