#include <iostream>
using namespace std;

int main() {
    int X,Y,Z,sunuke;

    cin >> X >> Y >> Z;
    sunuke = (Y * Z - 1)/ X;

    cout << sunuke << endl;
}

#include <bits/stdc++.h>
using namespace std;
#define pp pair<int,int>
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rep2(i,m,n) for(int (i)=(m);(i)<(n);(i)++)
#define ll long long
#define ld long double
#define all(a) (a).begin(),(a).end()
#define mk make_pair
ll mod=998244353;
int inf=1000001000;
ll INF=1e18+5;
ll MOD=1000000007;
int main(){
  int a,b,c;
  cin>>a>>b>>c;
  cout<<21-a-b-c;
return 0;
}
