#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%x==0){ n+n-y/x ; } else{ n=n-y*x-1; } if(n<0){ cout<<0; } else{ cout<<n; } return 0; }