#include <iostream>
using namespace std;
void bep(int a, int b, int c){
int count;
while(1){
count++;
if(c-b <= 0){
cout << "-1";
break;
}
else{
cout << count;
break;
}
}
}
int main() {
int a, b, c;
cin >> a >> b >> c;
bep(a,b,c);
return 0;
}
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