Римские цифры

#include "stdafx.h"
#include <iostream>
using namespace std;


int main()
{
    int N, i, S, p, J;
    cout << "Vvedite kol-vo bykv ";
    cin >> N;
    J = 0;
    S = 0;
    p = 0;
    char b;
    for (i = 0; i < N; i++) {
        cin >> b;
        J = p;
        switch (b) {
        case 'I':
            p = 1;
            break;
        case 'X':
            p = 10;
            break;
        case 'L':
            p = 50;
            break;
        case 'C':
            p = 100;
            break;
        case 'D':
            p = 500;
            break;
        case 'M':
            p = 1000;
            break;
        case 'V':
            p = 5;
            break;
        }

        if(J>=p)
        S = S + p;
        else {
        S = S - J+(p-J);
        }

    }

    cout << S;
    system("pause");
    return 0;
}