解：

#include <iostream>
#include <string>
using namespace std;
int main() {
    int n, m;
    string a;
    cin >> n >> a >> m;
    if (m < n && a[2 + m] >= '5') {
        for (int i = 2 + m - 1; i >= 2; i--) {
            if (a[i] < '9') {
                a[i]++;
                break;
            } else {
                a[i] = '0';
            }
        }
    }
    cout << a.substr(0, 2 + m);
    return 0;
}