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OI-codes/Luogu/T160507/T160507.cpp

15 lines
251 B
C++

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