文件目录

#include <iostream>
using namespace std;
int main()
{
    int a, b, m, n;
    cin >> a >> b >> m >> n;
    int sum = a + b;
    for (int i = 3; i <= n; i++)
    {
        int c = a + b;
        sum += c;
        if (c >= m)
            break;
        a = b;
        b = c;
    }
    cout << sum;
    return 0;
}