#include <stdio.h>
#include <functional>
#include <algorithm>

int main() {
    int l, r, m; scanf("%d%d%d", &l, &r, &m);

    std::function<int (int, int)> solve = [&](int l, int r) {
        l %= m; r %= m;

        if(l <= r) return r - l + 1;
        return r + (m - l + 1);
    };
    printf("%d\n", solve(l, r));
    return 0;
}