#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int n,x,y; cin>>n>>x>>y; if(y%2==0){ n=n-y/x; } else{ n=n-1-y/x; } if(n>0){ cout<<n; } else{ cout<<0; } return 0; }