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#include <iostream>
#include <cmath>
using namespace std;
int main() {
    int n, k = 3, count = 0;
    double ak, ak_1 = 3, ak_2 = 2, ak_3 = 1, s = 0;
    cout<<"n = ";cin>>n;
    while(n<=3)
    {
        cout<<"n = ";cin>>n;
    }
    cout<<"k = ";cin>>k;

    do
    {
        ak=sin(3.14/k*ak_2) - ak_1;
        ak_3=ak_2;
        ak_2=ak_1;
        ak_1=ak;
        count++;
        k++;
        s += ak;
    }
    while(k<=n);
    s /= count;
    cout<<"SA = "<<s;
    return 0;
}