#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define fast ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#define cap pair<int,int>
#define fi first
#define se second
#define pb push_back
#define FOR(i,l,r) for(int i=l;i<=r;i++)
#define FOD(i,r,l) for(int i=r;i>=l;i--)
#define fill(f,x) memset(f,x,sizeof(f))
#define lcm(a,b) (a/__gcd(a,b)*b)
#define TIME 1.0 * clock() / CLOCKS_PER_SEC

signed main()
{
    freopen("CAU1.INP","r",stdin);
    freopen("CAU1.OUT","w",stdout);
    fast;
    int x1,x2,a;
    cin>>x1>>x2>>a;
    int cnt=0;
    while(x1<x2)
    {
        x1+=a;
        cnt+=1;
    }
    cout<<cnt;
    return 0; 
}