#include <bits/stdc++.h>
using namespace std;
int main(){
	int t[10001],l[10001],v,n,c,ans=0;
	cin>>v>>n>>c;
	for(int i=1;i<=n;i++){
		cin>>t[i]>>l[i];
		if(l[i]>=c){
			l[i]--;
			ans+=l[i];
		}else{
			cout<<"Impossible"; 
		}
	}
	cout<<ans;
	return 0;
}