16 lines
274 B
C++

#include<iostream>
#include<cstdlib>
using namespace std;
int main()
{
long k,a,b,c,i;
cin>>k;
if (k==1) cout<<1;
else if (k==2) cout<<2;
else { a=1; b=2;
for (i=3; i<=k; i++) { c=a+b; a=b; b=c; }
cout<<c;
}
return 0;
}