#include<iostream>
#include<cstdio>
using namespace std;
double m,t,s,a,b,y;
int main()
{
cin>>m>>t>>s;
if(t==0) y=1;
else y=1.0/t;
a=y*s;
b=m-a;
printf("%.0f",b);
return 0;
}