#include <bits/stdc++.h>
using namespace std;
int main() {
    long long l, r, m; cin >> l >> r >> m;
    long long d = (r - l) / m;
    l %= m; r %= m;
    if (d) cout << m << endl;
    else {
        if (l < r) cout << r - l << endl;
        else cout << (m - l) + r + 1 << endl; 
    }
    return 0;
}