#include <iostream>
using namespace std;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int a, b, k;
    cin >> a >> b >> k;
    int c = 0;
    if(a != 0 && b - a >= k){c++;}
    cout << ((b - a) / k) + 1 - c;
    return 0;
}