#include<bits/stdc++.h>
using namespace std;
int main(){
    int n, m, p;
    cin >> n >> m >> p;
    float s = (n - m) / p;
    if(s - (n - m) / 1.0 * p > 0) cout << (n - m) / p;
    else cout <<  (n - m) / p + 1;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main()
{
	int n,m,p;cin>>n>>m>>p;int ans=0;
	for(int i=m;i<=n;i+=p)ans++;
	cout<<ans;
	return 0;
}