#include   <stdio.h>
#include  <locale.h>       //  здесь "живёт" setlocale(LC_ALL, "rus");


/////////////////////////////////////////////////////
int main()
{

    setlocale(LC_ALL, "rus");

    int n       = 0,
        nSerial = 0,
        nOstato = 0,
        nSumma  = 0;

    printf("Введите количество книг: ");  scanf("%d", &n);

    nSerial = n / 7;   //   printf("nSerial = %d\n", nSerial);
    nOstato = n % 7;   //   printf("nOstato = %d\n", nOstato);

    //

    switch(nOstato)
    {
        case  0: nSumma =    0;  break;
        case  1: nSumma = 1000;  break;
        case  2: nSumma = 1945;  break;
        case  3: nSumma = 2835;  break;
        case  4: nSumma = 3670;  break;
        case  5: nSumma = 4450;  break;
        case  6: nSumma = 5175;  break;
        case  7: nSumma = 5845;  break;
    }

    nSumma  =  nSumma + (5845 * nSerial);                  // nSumma  += 5845 * nSerial;

    printf("Общая стоимость %d книг = %d\n", n, nSumma);

return 0;
}