WA on #41

#include <bits/stdc++.h>
using namespace std;

int a, b, c;

int cal(int a, int b) {
    return (b-a)/2+(b-a)%2;
}

int main() {
    cin>>a>>b>>c;
    
    if(b<c) {
        cout<<cal(a, b);
    }else if(c%2==0 && a%2==1) {
        cout<<cal(a, b);
    }else if(c%2==0 && a%2==0) {
        cout<<cal(a-1, b);
    }else if(c%2==1 && a%2==0) {
        cout<<cal(a-(b-a)/c, b);
    }else if(c%2==1 && a%2==1) { // 问题大概在这里，调不出来了
        cout<<cal(a, b)+(b-a)/c/2;
    }
	return 0;
}