// yukicoder
#include <bits/stdc++.h>
using namespace std;

int main()
{
    int a, b, n;
    cin >> a >> b >> n;

    vector<int> vec;

    for (int i = a; i <= b; ++i) {
        int tmp = i % n;
        vec.push_back(tmp);
    }

    set<int> ans(vec.begin(), vec.end());

    cout << ans.size() << "\n";

    return 0;
}