#include <iostream>
using namespace std;
typedef long long LL;
int main(int argc, char* argv[])
{
	LL L,R,M,i;
	cin>>L>>R>>M;
	if (M>R){
		cout<<R-L+1<<endl;
		return 0;
	}
	if (L==R){
		cout<<1<<endl;
		return 0;
	}
	LL x0=L%M;
	//cout<<x0<<endl;
	LL Num;
	if (M<=L){
		Num=1;
	}else{
		/*for (i=L+1;i<M;i++){
			cout<<i%M<<endl;
		}*/
		Num=M-L;
		L=M;
	}
	for (i=L;i<=R;i++){
		LL x=i%M;
		if (x!=x0){
			//cout<<x<<endl;
			Num++;
		}else{
			break;
		}
	}
	cout<<Num<<endl;

	return 0;
}