#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ull unsigned long long

using namespace std;

const int N = 5e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

LL a, b;

int k, lcm = ;

int dp[N];

void getDp(int x) {

    memset(dp, -, sizeof(dp));

    dp[x] = ;

    queue<int> que;

    que.push(x);

    while(!que.empty()) {

        int u = que.front(); que.pop();

        if(dp[u - ] == -) {

            dp[u - ] = dp[u] + ;

            que.push(u - );

        }

        for(int i = ; i <= k; i++) {

            int v = u - (u % i);

            if(~dp[v]) continue;

            dp[v] = dp[u] + ;

            que.push(v);

        }

    }

}

int main() {

    scanf("%lld%lld%d", &a, &b, &k);

    swap(a, b);

    for(int i = ; i <= k; i++)

        lcm = lcm / __gcd(lcm, i) * i;

    LL ans = ;

    LL R = b - (b % lcm);

    LL L = a + (lcm - a % lcm) % lcm;

    if(L <= R) {

        LL cnt = (R - L) / lcm;

        getDp(lcm - );

        ans = dp[] * cnt + cnt;

        if(a % lcm) ans += dp[a % lcm] + ;

        getDp(b % lcm);

        ans += dp[];

    } else {

        getDp(b % lcm);

        ans = dp[a % lcm];

    }

    printf("%lld\n", ans);

    return ;

}

/*

*/